I once arrived at an IFR equipped, twin engined helicopter which had a very much depleted battery due to certain unqualified people having “fiddled” with the systems for some time and subsequently not realising that plugging in an external power supply disconnects the aircraft battery from the system, rather than charging it...
Having pointed out the situation, I was then told to fly said helicopter to a maintenance place to get the battery swapped for a good one. Bearing in mind that the engines were DECU only, with no manual backup and didn’t have their own generators and the cloud base was well below 500 feet, I made myself extremely unpopular by refusing. An engineer with a new battery had to be dispatched by road.
A double generator failure with a failed battery (or even a cooked battery due to overcharging in flight) could have found me with no flight instruments, no engine control, or a battery fire.