A couple of other thoughts that spring to mind -
1. Pressing on with a start with a low voltage battery can not only lead to hot starts, but if you do get it going, a depleted battery will suck lots of current which may then increase the chance of a thermal runaway. Best to forget about the start and change the battery if you can.
2. If memory serves me correctly, a very depleted nicad can have internal reversal of polarity within individual cells, which can set up a situation where the cells are feeding eachother - high current causing high temp, and with a generator to keep pumping current in, it will quickly lead to the hot kaboomish situation described above.
Recuperator, hopefully you can convince your colleague that a hot battery can turn pretty bad pretty quick!