[trit21]

If you place 5 temp sensors, one on each battery, then the battery charger sense excessive heat it will shut down the charger. I don't think your looking at this quite correctly though. You lost a cell probably due to lack of water which then the charger tired to overcharge. Well, if you don't fill one cell on the ONE battery guess what, the charger will still try to overcharge the battery and this time if you have a problem with one battery you only have one so it will have to be replaced. At least with 5 batteries if you catch it in time you can just take it out of the loop and you are good to go.