You may consider that I should pose this question on an Aviation Forum, but I reckon I'll get more response from the general Intelligentsia who know about battery charging and things electrical ?
My Aero Club have a handheld radio to talk to the pilots, especially for instructors to monitor the progress of new students flying solo for instance.
The radio has a NiMH battery pack containing half a dozen cells that has recently had to be re-packed with new cells because the original ones died.
As the club is not occupied constantly, and the radio may be required without previous advice to ensure that it is charged when irregularly needed, it has been our habit to leave it permanently slotted into the charger unit connected to a nearby live wall outlet - against the advice of the Manual which advises against constant charging in excess of 24 hrs. ( RTFM )
Not wishing to damage a new battery pack, what is the best way to ensure that the radio is always charged and ready for infrequent use ?
When fully charged we are considering a time switch to provide - say - 1 hour charge every day, regardless, but is attempting to recharge an already fully charged battery, even for a short time, going to damage the battery cells again ?
I think you're on the right track there.Maybe 30 minutes of timer charging a day.According to Wiki,they lose 5-20% of the charge after the first day but then stabilise to 0.5-4% per day thereafter.As for damaging a fully charged battery,it depends on what sort of charger you have.If it's a 2 or 3 step 'intelligent' charger that senses battery voltage,it won't overcharge the battery.If it's a cheap charger with no 'smarts' such as supplied with cheap cordless drills etc,then it may shorten the lifespan of the battery by overcharging.No way to predict in that case.
Buy a second set of batteries and have one lot charging on a timer while the others are in the handset, draining down as normal. When the ones in the handset get low, swap them over, thus keeping the charge/discharge cycle going. You will also have a fully charged set on hand, if needed.
This would only work though, if the batteries can be charged separate from the transceiver.
If the radios are switched off the rate off discharge say for one week should be hardly noticeable so you only need to ensure they are charged during and when you've finished for the day, so all you need is a timer that is set for a one off shot of say 12 hrs which is set when you go home.
Used to have the same problem, all sorted out by using pre-charged ready to use NiMH Accus cells. They come pre-charged and have a very low self discharge rate, still usable after a year. Use them in my noise canceling headset, no problem with intermittent use.
AS an alternative, why not try some of the hybrid batteries, such as the Sanyo Eneloop, or Ansmann MaxE?
These will charge using a normal NiMh charger but, typically, only lose 5-10% over the course of a year, with a recycle life of 1500 - it would certainly solve the problem of needing a radio to be usable at short notice.
Incidently I have a hand-held ATC radio in the car which is used rarely and I only use good quality replacable, not rechargable, batteries in that, and keep a spare set handy. (It also beeps when it gets hungry).