View Full Version : Car battery question.

13th Jun 2014, 01:32
Just about to leave my car for 3 months, a Honda Accord Euro, full of all today's computerised garbage.

The battery is only 6 months old and in good shape, and will "probably" be OK, but in the Good Old Days I'd have discnnected it anyway, but I don't want to go to the hassle of having to re-programme everything just to have to start the car, radio, security stuff etc. when I get back if I do that.

I have an ancient trickle charger that has served me well, and which I occasionally connected whilst away, but I'm told that the new, sealed, batteries don't like them, and I should buy a highly expensive "intelligent" charger instead. Not going to.

Question - I have a fairly simple, small, Solar Panel that pushes out about 16 volts on a good day, and am considering leaving it connected to the battery - is this dangerous, computer and modern batterywise ? Can I connect via the cigarette lighter / 12 v. power socket, the cell has a male cig. lighter end on it, i.e. does the charge go backwards up the cig. lighter circuit when everything is switched off, or should I connect it directly to the battery terminals ?

Life used to be simpler before computers.

Any advice, experience appreciated, thanks.


13th Jun 2014, 01:59
I have a friend with a modern car who lives on an island and can go for a week or two without getting to the (which mis parked on the mainland) car.
He has (as do you) a small solar cell array that is always plugged in (to the lightersocket) and this keeps up with the natural drainage of the system.
He has had no problems whatsoever, so I would say just go ahead and use yours.

13th Jun 2014, 02:46
Many car lighter sockets are 'off' when the ignition is off, so check this on your car, as there is no point in having power being fed in here when the circuit is not active. My preference would be to leave the trickle charger connected, but wait until you get some answers here from people who know electrickery better than me.

13th Jun 2014, 03:02
In some/most modern cars the cigarette lighter socket is only active when the ignition switch is on.

This means that charging the battery via the cigarette lighter socket would also require the ignition to be on for the circuit to be complete. If this is case with your vehicle, a connection directly to the battery would be needed. Ideally anything so connected needs a fuse in the supply line so that in the (unlikely) event of a short circuit in the equipment, other potential disasters are prevented.

There seems to be no clear consensus whether a regulator and/or blocking diode is needed when a small solar panel is used in such a situation. Some panels may already have the blocking diode installed. (The reason for such a diode is to prevent a slight discharge from the battery back though the solar cells at night time). Several articles suggest that it's not significant in most situations. If there is a controller / regulator in the solar package, this should be managed automatically.


13th Jun 2014, 03:12
I would go to the battery.

My small panel has a diode in it to stop leakage as per post above.

I have known some people to connect a very small light globe to the battery so it cycles down a little bit each day and of course the solar panel charges it up again.

This was before modern cars that obviously use electricity more than old one did.

A A Gruntpuddock
13th Jun 2014, 03:36
My car was left in the garage for an extended period and the battery ran down.

It charged up OK, but the ignition immobiliser acted up.

Car started the first few times but next day it was dead - car had to be scrapped.

Might be worth seeing if there is any procedure you can follow to prevent this happening in case your recharging system stops working.

13th Jun 2014, 03:54
AAG - Your battery ran down and you scrapped the car?? That's a little extreme isn't it?? I mean to say, I've heard of blokes selling their car when the ashtray got full, but scrapping it when the battery ran flat?? ... :rolleyes: :E :p

13th Jun 2014, 03:55

I was wondering the same thing.

Lon More
13th Jun 2014, 04:08
If I leave my car for a couple of weeks the alarm drains the battery. No cigarette lighter per se but a couple of accessory sockets, front and rear, always live, and not through the canbus, that I can plug the solar panel into

13th Jun 2014, 04:22
ExSp33db1rd - There are a couple of things we'd need to know, to supply a complete answer.

1. What is the output of your solar charger?
2. Does it have any controlling or switching apparatus built in, to switch off charging when the battery is fully charged?

Lead acid batteries in cars today are generally semi-sealed, low-maintenance, lead-calcium hybrids. They don't like being overcharged.
Charging voltage is critical, it needs to be kept strictly to 2.25V to 2.30V per cell.

A fully charged car battery in good condition should store admirably without charging for 3 mths, provided there's no drawdown.
However, 0.35A is a common parasitic drawdown figure for a connected battery in a car that is parked up.
This means you'll need to trickle charge at that rate constantly - or at a higher intermittent rate, with regular shutdowns when the battery is fully charged.

Overcharging LA batteries generates heat and gassing - and current L-C-H car batteries don't cope with gassing very well, because they either have no venting, or very limited venting.
Thus the case for "intelligent" chargers.
For the cost of a small intelligent charger, I'd be investing in one.

This following website is very informative about every type of battery known.

Battery Information Table of Contents, Basic to Advanced (http://batteryuniversity.com/learn/)

13th Jun 2014, 04:38
Connect your "primitive" charger to the battery cables, but disconnect them from the battery (actually only the negative one). This will supply the power to the parasitic circuits and keep the battery udrained. You only run a risk of losing your radio and other settings if during your absence main power fails.

13th Jun 2014, 07:04
Onetrack 1.What is the output of your solar charger?
2. Does it have any controlling or switching apparatus built in, to switch off charging when the battery is fully charged?1. No idea.
2. ditto, but none apparent.

In bright sun it produces a "cycling" range of voltage readings from 4v. to 16.v, and in cloudy conditions it barely reaches 9v., measured on a cheap multi-meter, so I don't think it will do any harm, confirmed by a phone call to the local Auto Electrician, but again - who was I talking to and what was his experience ?

Just as easy for me to go direct to the battery terminals,and ignore any on board 12v sockets, so at least I'll do that.

Disinclined to disconnect the battery, tho' I appreciate the theory, in fact aforesaid Auto Elec. admitted that they clip a dry cell 12 v battery to the battery cables when they change a battery for that very reason, but at night - with no solar voltage - and with the battery disconnected the computer stuff may just sat "Sod it" and switch off anyway,which I'm trying to avoid.

Course - I could just read 'The Book' and learn how to re-programme everything, but the Gruntpuddock experience scares the pants off me - it's Mrs. ExS's car - I'm just going to disengage the battery on mine, being a 22 yr. old "basic" car with a battery that one can re-charge and top-up with impunity.

Except that -- last time I disconnected, I turned up back at the airport and couldn't start - flat battery. I organised a drive-by start facility, and when we opened the bonnet to connect the jump leads ................. I saw that the battery had been disconnected !! I'd forgotten !! ( at least I'd remembered where I'd parked it, which was a bonus. )

I may go the "Intelligent" charger route after all, as you say, in the overall scheme of things the cost is hardly worth belly-aching over. ( but why do THEY have to keep changing things ! I had total control over my Dad's 1935 Morris 8, even had a staring handle if things got out of hand, and I even managed to get a speeding ticket on that, never mind today's Rocket Science jobs. )

Thanks for all the tips.

13th Jun 2014, 07:11
... Disinclined to disconnect the battery, tho' I appreciate the theory, in fact aforesaid Auto Elec. admitted that they clip a dry cell 12 v battery to the battery cables when they change a battery for that very reason, but at night - with no solar voltage - and with the battery disconnected the computer stuff may just sat "Sod it" and switch off anyway,which I'm trying to avoid...

That will definitely happen - the electrics all go to sleep when they are not being fed 12v (or at least something close to it) - and probably night 1 :*. Good thing is it won't spoil your holiday as you won't know until you return, so you will have a holiday in blissful ignorance of what awaits :ok:

13th Jun 2014, 07:18
An option may be to use your current (ha - see what I did there :O) trickle charger through a 24-hour timer (not a digital one that might lose settings in case of a power failure, but an electro-mechanical one). If you set the trickle charger to run for 30 minutes a day it should just top up what the parasitic loss is. Maybe even 15 min in each 24 hr cycle will work fine. I think this will avoid overcharging. (And remember, my advice is worth every $ you paid for it :8)

13th Jun 2014, 07:28
I very cleverly chose to pack one of those cool boxes with a cooling plate built in, on the night before the departure for a vacation trip. Then I connected it to the power point at the back of the car, but connected a trickle charger to the battery under the bonnet. Sorted! Well, except for the fact that the cool box took a bit more out than the charger put back in .... It is a real hassle, finding that little slip of paper with the code for the radio, after already having to have a dead battery replaced at the last minute before a long trip.

I would go for the intelligent charger and leave it at that. Or else, simply disconnect the battery, after first finding that paper with the code for the radio. You might still need a new battery, depending on how long you are away, since batteries lose charge just sat there, and these things with the calcium chemistry, when they go dead, we are not speaking of Lazarus. If the price of the intelligent charger is about the same as the cost of a new battery, well, there is your answer.

Nervous SLF
13th Jun 2014, 07:32
Why not give Honda a quick call as they will know much better than people on here I would have thought? You could also
have a look here :- Honda - Automotive - Whirlpool Forums (http://forums.whirlpool.net.au/forum/133?&g=270)

A A Gruntpuddock
13th Jun 2014, 08:06
I scrapped the car because, as I stated, the ignition immobiliser prevented it starting.

Local motor electrical guys spent a week trying to fix it but to no avail.

Only way forward was to try a new circuit board and, even if they were still available, there was no guarantee that it would cure the problem.

Cost of the components alone would exceed the value of the car so it had to be scrapped. :sad:

13th Jun 2014, 08:49
It might be worth checking with Honda to see if disconnecting the battery will in fact cause the radio settings etc to be lost. After reconnecting the battery on my VW the radio does a security 'handshake' with the car's ECU which recognises that the radio uniquely belongs to my car. After a few seconds the radio automatically returns to its previous state including all preset radio stations. The only thing I had to reset was the LCD digital clock.

13th Jun 2014, 09:10

Do you have the option of leaving a set of keys with a friend? They can take it for a wee spin once a week to keep things topped up.

13th Jun 2014, 10:00
While the idea may seem entirely logical and sensible, I would very much recommend against connecting a trickle charger direct to the car without the battery also being in the circuit.

I have such a device which pushes out over 16 volts with no load and this does not reduce to 13.8 volts - a typical value to be found on a modern horseless carriage while the battery is being charged - until the load is 78 ohms which represents a current draw of 176 milliamps.
There is also the possibility of very small and short spikes of greater voltages being induced by the charger at anytime of connections being made or broken.

Even such momentary transients can easily damage or destroy some of these new fangled electronic gadgets which are often found to be very poorly protected against such grief.

The electrical load of the battery acts as a very substantial buffer to any such interferences and will ensure that no such higher-than-normal voltages can penetrate the system.


13th Jun 2014, 10:34
Why not give Honda a quick call as they will know much better than people on here I would have thought?Did that, a "girl" was pleased to answer my question after discussing the issue with their technician, and no, the cig.lighter socket would not work "backwards", and no, they couldn't advise about a solar charger as they knew nothing about my charger so wouldn't commit themselves, but it was essential to drive the car every two or three weeks to avoid the tyres setting into "flat spots", so that would take care of the battery discharging issue as well. Anything else we can help you with, Sir? Thank you for calling Honda Technical dept. At least I was only making a local call to Auckland, not Tokyo.

Do you have the option of leaving a set of keys with a friend?Probably, except that shoe-horning the car in and out of the over stuffed garage is an exercise kept solely for rare occasions like this, and the thought of someone else attempting it would give Mrs. ExS the vapours !

It might be worth checking with Honda to see if disconnecting the battery will in fact cause the radio settings etc to be lost.The local Honda dealer fitted a new battery a little while ago, and did the trick of hitching up an auxilliary battery as he swapped over them over, then discovered that his aux. battery was dead, but in fact the radio had not lost it's code, he reckoned that there is a small buffer of a few minutes before it throws in the towel, and we made it in time. Dunno.

Thanks again for all the comments, got a few days to consider my options !

Friend in the USA has a Honda on a leasing deal, which avoids all this, she justs throws the car back at them when she goes away and picks up another one on return !

13th Jun 2014, 10:55
It charged up OK, but the ignition immobiliser acted up.

Car started the first few times but next day it was dead - car had to be scrapped.

Inside the 'brain ' of the car and the 'brain' of the immobiliser there is a small button cell that holds the original coding if the main battery is lost for any reason. These cells hold the original information for months on end when new. As they age however,their capacity drops off,and at about 15 years old they lose all the programmed info in quite a short time. If you leave the main battery off for too long they lose their programme completely. Same as a computer.Is can lose everything,including it's windows or whatever if left with the main battery flat.:ugh:

13th Jun 2014, 11:33
Lots of options canvassed during the day; the extra information has been helpful.

On balance I would now support the use of a dedicated "intelligent" charger connected directly to the battery, with due care not to pinch the leads or let the clips touch anything which could cause a short on the DC side.

I use one of these (http://www.jaycar.co.nz/productView.asp?ID=MB3604&form=CAT2&SUBCATID=998#3) for my motor bike battery. I have also used it for longer term top up of larger batteries in use for other (amateur radio) applications. It takes a while to top up a N70ZZ, but it will do it. It would also very suitable for applications along the lines of what you are proposing.

There is a less expensive model (http://www.jaycar.co.nz/productView.asp?ID=MB3603&form=CAT2&SUBCATID=998#12) which may well do the job, but it's maximum charging current is only 750mA, however this would be adequate if you only have the stated requirement and nothing else.

No particular recommendation here, just advising what I have found to be useful - and available on your side of the ditch as well. :)

13th Jun 2014, 11:53
After fully charging the battery and then disconnecting the leads, I leave my 2011 Hyundai Elantra garaged for 7 months every year. No other charging. No problems whatsoever apart from resetting the clock. One other reset, required only twice was an anti-skid or traction control ( I cannot remember which) all this requires is moving the steering to full lock left then right.
I also jack up the wheels off the ground but I understand with modern tyres this is no longer necessary.

13th Jun 2014, 12:37
There are quite a few battery tenders available, thatwill look after your car if left for a considerable time. Its not a charger as such, in that it monitors the battery, gives it a trickle charge now and then and a small discharge. Lead acid batteries hate sitting idle for extended time periods.

The acid in a sitting battery attacks the plates, giving a coating of lead sulphate. Its insoluble, and pretty much protects the lead from further acid attacks ( and renders battery useless).

A battery needs to have some sort of charge/discharge to stay healthy. Even the modern totaly sealed battery needs a little activity stay healthy.

The Flying Pram
13th Jun 2014, 12:39
As already discussed, you need a regulated charger which won't go above 13.8 (ish) volts, regardless of how long it's left connected. If you don't mind a bit of experimentation, domestic burglar alarm panels invariably have a small sealed lead acid battery maintained by a mains - DC charger. If you can get hold of one of these, and either 1) keep it in the original case, or 2) mount the charger circuit board in a suitable EARTHED box, you could use that. As you aren't trying to re-charge or recover a flat battery, the sophisticated multi-step chargers are simply overkill, and all you require is a single stage unit such as I've indicated above. In the UK companies such as Maplin, RS etc sell small standalone chargers similar to this, for less than 20 or so.

Secondly, if you use a solar panel you MUST fit some sort of regulator, as the voltage on a sunny day could easily rise above 16 volts or more. For the size of panel you are probably thinking of (5- 20 watts?) this can be as simple as a single Zener diode, of at least the output rating of your panel, and connected in parallel with the panel output leads. In this situation it will do nothing until the voltage reaches the predetermined value, then it begins conducting, and just turns the excess energy into heat. They normally come in increments of about 1volt, so choose one of no more than 14v - car alternators typically go up to 14.5v and some newer ones 15v, so 14v is perfectly safe, considering it will only reach that on sunny days, and then for a few hours at most. Zeners are available from electronic component suppliers - usually up to 5watt rating they will be a simple plastic package with wires each end. Larger ones are typically stud mounted to facilitate attaching to a heat sink. They will get hot, when doing their job, so beware! Also note that the polarity has to be correct or they will act as a short circuit. Try it on the panel before connecting to the battery, and monitor the voltage with a meter. Connect directly to the battery with insulated Croc clips - a small fuse in-line is also a good idea.

Disclaimer: any experimentation as described above is at your own risk!

13th Jun 2014, 12:48
Connect your "primitive" charger to the battery cables, but disconnect them from the battery (actually only the negative one). This will supply the power to the parasitic circuits and keep the battery udrained. You only run a risk of losing your radio and other settings if during your absence main power fails.

Big No No to this. The charger will produce a ripple current without the battery connected, this may damage some modules on the car.

Buy a proper automatic float charger or just disconnect the battery and suffer the reprogramming later (10 mins?) would be my advice.

Most battery chargers on sale will be "automatic" and suitable to maintain a float charge - I have a vehicle that sits up for months on end with a non fancy 50 buck automatic charger attached, works fine.

13th Jun 2014, 13:12
Heading off for a couple of months soon and have just learnt to put up with a radio, clock, etc needing to be re-setup again when I get back. Sometimes it can take a few weeks for me to get around to all of them.

I now disconnect both terminals and charge up the battery which is the most safest, most cheapest and most inconvenient option.

Leaving a mains fed battery charger connected and unsupervised is a potential fire hazard - I've had one such battery charger cook itself, but it was a cheapie.

A basic 12v power adapter connect where the battery used to be would probably hold fine for a few days but you got to wonder whether the manufacturers actually designed the power adaptor to run continuously for a couple of months, and if there is a domestic power failure then you've achieved nothing.

I've never used a solar charger before but I recall a bloke down the road had one connected one year, then the next year he had shoved a mains fed battery charger under the bonnet. But I don't know the full story, maybe his battery was on the way out anyway.

Good luck, and try not to worry too much about it until you get back.

13th Jun 2014, 15:38
Frequently Asked Questions | Honest John (http://www.honestjohn.co.uk/faq/storing-a-car)

13th Jun 2014, 17:29
Just leave your car at one of the recently shamed off airport car parks and I am sure that they will make sure the battery remains charged by regularly driving it about.

13th Jun 2014, 20:52
I've got a 2 litre Kia Ceed Sport SW, just 5 years old and the battery failed over Christmas. It's just coming up to 22,000 miles, so, bit of a shock. (Fab car though) Having personally been around for about 308,000 miles using the same criteria, my battery is still going good. Just needs a regular top-up with Strongbow, say 30 cans a week and little exercise as both big and little ends have gone.

Under NHS rules don't qualify for any universal joint replacement yet, but still can achieve nearly 4 miles per hour on good days. Crankshaft a little worn and number one piston broke, but only once a month on average!

Body finish still pretty good but surface wrinkling due to exposure to elements. Ceed had 4 new top quality feet a year ago, still got little rubber nobbles hanging here and there, but we all have, haven't we?

Personally pair of M&S all leather shoes obtained 2 years ago are wearing thin after only 100 miles.

As an old fogy who many years ago sat astride his Morris engine (no, I'm not like that at all) and played with it's bits, I just don't do that any more....I just have to pay somebody else to play with my bits and at an extortionate cost, if I still wish to drive!

The moral is, don't invest in a new car, get a new body!

13th Jun 2014, 22:03
piston broke

Yeah - me too.

14th Jun 2014, 01:02
Had to get rescued by the fine folk of the RAC, when my new security system I devised to prevent thieving sods nicking my car, whilst surfing alone. The old "leaving the key on top of the wheel" is not appropriate, as local reports suggested that people were being targeted. In fact the week before, two vehicles were stolen from stupid people from London who thought this was okay.

Looked at various options, and even posted a query here. Mr Draper suggested wrapping sophisticated immobilising key in a double wrapped condom, which admittedly did protect it, but left a poking feeling in the chest of myself and Mrs Ginger.

Problem is, surfing alone requires placing key in a place of safety. Local bars are happy to take in keys, then it all get a bit corporate, so they started refusing, insurance and all that.

Some contempories bought mini safes that hung from the bottom of the wish bone, but, as my insurance company stated that they wouldn't pay out if the car was stolen with the key, this made me more nervous.

The only solution, was to drive down to the beach car park, change into the wetsuit, unleash the board from the rack....and, (this is the clever bit) don't lock the car, but place Hound Max, on top of the key for safety. For extra protection, place it under the back floor mat.

Unfortunately Max manaed to double lock the car. Hence the call to the RAC (shivering in a cheap wet suit, and guess what, my phone was in the car.)

Finally, getting back to the point of the story, about how to keep the car battery in tip top condition and all that, when it's switched off, and where to place the trickle charger, the RAC guy had a bit of a challenge on his hand, Max managed to "double lock" the car, RAC man had to somehow tap into the power supply to unlock the mechanism. He jacked up the car, and attached a "live" to the reversing switch, and bingo.....we rescued both dog and car.

The culprit.........


14th Jun 2014, 01:22
Since you have access to the electrical grid the easiest is to get a multi stage "smart" charger available for sub NZD100. I've used one on my motorbike for years and it's cheaper than buying new batteries regularly.

If no access to the grid go solar. I use a small solar panel, (5 watt) on my yacht starting batteries. Such a small wattage does not need regulating, according to my solar specialist supplier, and I have had no problems over the seven or eight years I have done this. In fact the batteries are still fine after all this time and I doubt they would be otherwise.
One note of caution, perhaps the capacity of the battery may have some bearing on whether a 5 watt panel would be too much. You should be able to get a panel and a smart solar regulator for sub NZD100 as well.

14th Jun 2014, 03:21
modtinbasher - It's been noted that todays vehicles have a substantially larger drawdown on batteries as compared to vehicles of even 20 yrs ago.

Ever-increasing levels of electronics, in the form of electrically-operated power steering, ABS, anti-swerve systems, airbags, reversing cameras, reversing sensors, nav aids, amongst many other device demands, are all placing a heavy load on batteries that have not increased in size to cope with the extra electrical load.
Where this does show up is when a vehicle is used for mostly short trips - and often with lights on as well.

With short trips, there is inadequate recharge time available for the battery, despite the alternator working at full output.
The cure is to ensure you regularly go for a longer drive at modest speed to ensure the battery gets adequate recharge time - or attach a trickle charger weekly, to give the battery a full charge.

14th Jun 2014, 03:31
On my boat, I've connected the (built in) charger via a time switch on its 13 amp socket. The timer is set to come on for an hour each on mon, wed and fri. Batteries (4) used to run down but not any more.

17th Jun 2014, 05:59
Thanks guys, opinon seems to be that I'll just disconnect the battery and take pot luck.

Watch this space - in 3 months time !

17th Jun 2014, 07:23
todays vehicles have a substantially larger drawdown on batteries

True, but with 68% of the cars here being diesels, they also have larger batteries, and the old lead-acid are a thing of the past, at least in Fords over the past eight years.

17th Jun 2014, 08:34
I used to leave my Hyundai Sonata out in all weathers for two months at a time. The doors would unlock and the car would start immediately. It's got as many gizmos as any other car.

17th Jun 2014, 11:59
............but the driver's door CAN be manually unlocked.

If you can remember where you put the key.

First trip ever to New Zealand, hire car, deserted beach ( all beaches are deserted in NZ ) night falling, old fashioned car - i.e. no computer - no central locking.

Took off jacket for walk along the beach, threw it through the door, pushed the button down on the last door and slammed it - F**k it, keys in jacket pocket.

Only one house in sight, knocked on door, tremulous 12 yr, old girl peered through the glass followed by Dad, who angrily asked what did I think I was doing disturbing his daughter at this time of night ? After explanation, Dad and I attacked the car with the trusty, rusty, wire coat hangar, attempting to hook the lock button and release it.

About 30 minutes later, now pitch dark, the 12 yr. old walked over to see what was happening, assessed the situation, then pushed the door firmly closed - it had only caught on the first safety latch, and the lock button popped up ! Problem solved.

Not A Lot Of People Know That - but no use on the present computerised, central locking, expensive electronic key nonsense. That's progress.

( Doesn't stop the car thieves, either, so what's the point ? )

17th Jun 2014, 12:52
I parked an Audi A3 outdoors at MUC airport from mid November to mid January. On return it was covered in snow and presumably had been for weeks. Cleared the snow from the driver's side, opened the door, key in lock, turned it, and within in a few seconds she fired and ran as smooth as silk on all cylinders.

Compared with a Fiat I once had, used to have to roll the bloody thing about a mile (luckily I lived at the top of town) until it fired.

My mother, who was a brilliant classicist but had no clue about anything technical, once told me that her car needed a new battery 'because it slows down going up hills.'