If one considers a battery connected to a battery charger to be a load, then the battery is a non ohmic load, and the current absorbed by the battery will vary in a non linear fashion with changes in voltage.
For example a 12 volt nominal battery would normally be charged at about 13.8 volts. Once the battery is fully charged then the current will be very small, perhaps 0.1 amp for a medium size battery.
If the charging voltage is improperly raised to say 16 volts, then a very great current will flow until either a fuse blows, or the battery, or the battery charger is destroyed.
If however one is altering the line voltage supply INTO a battery charger, then with most designs, a higher line voltage will result in a lower line current.
That is because most modern battery chargers use a switch mode power supply, which draws the required wattage at any line voltage, with the design limits of course.
For example if the battery charger requires 120 watts, then that will be about 1 amp at 120 volts, but only about 0.5 amp at 240 volts.
(this all presumes that the charger is designed for multi voltage input, if it designed for a fixed line voltage then it wont work properly or at all at the wrong voltage)
The correct charging voltage varies slightly with temperature, and should be less at higher temperatures.
The simple basic chargers, such as one might use at home for a vehicle battery, simply assume an average room temperature.
This is liable to result in overcharging in hot conditions, and in a less than full charge in cold conditions.
Larger more sophisticated battery chargers, as used for large UPS systems, measure the room temperature, or better the battery temperature, and adjust the voltage accordingly.
An excessive charging voltage or excessive temperature results in the battery still absorbing current when fully charged, this additional energy input turns into heat which raises the battery temperature.
This increased temperature results in more current, which raises the temperature even more.
If allowed to continue, disaster will assuredly follow.
The original cause of the problem could be
1) wrong voltage battery fitted, such as 108 volt instead of 120 volt
2) battery temperature sensor in the wrong place, perhaps detecting cold air from an AC unit rather than a warm battery
3)one or more cells in a battery failing, so that a nominal 120 volt battery is in fact, perhaps a 114 volt battery.
4)defective charger, as appears to be the cases refered to above.