I got a crash course on battery charging subtleties when building battle bots and there are many ways this can so south quickly, not the least of which is a battery in the middle of the pack developing dendrites and deciding its time to burn. The only way to prevent that is to have temperature sensors on every battery and a good enough model of the heat convection between the internal battery and the surface to recognize the temperature rise of a battery on its way to failing. Even with modern "battery monitor" chips like the ones Maxim and others sell there are corners in charge rate/temperature/battery that can get away from the algorithm before it recognizes a battery failure.
The reasons this is "easy" with flooded lead/acid batteries is that, when they fail, the lead doesn't then turn into a torch at 500 - 600 degrees F. So you have a chance to fix failures and move on.