Why my VRLA Lead-Acid batteries was thermal runaway (leakage even drum deformation)? How to solve it

In our experience, the mostly reason which caused battery overcharged and thermal runaway is “charger is not terminated just in time when battery nearly full charged and still apply higher voltage (>=14.0V for 12V battery unit)” To solve this thermal runaway issue, two solutions are accepted: The 1st solution is put an external NCT temperature sensor on the surface of battery, when battery get hot charger will cut-off output. The 2nd solution is use a correct timer to limit the high voltage (also called equalizing battery charger voltage) to a safe range. Solution one (use external temperature sensor) is precise, but need the charger give out and extra temperature sensor cable, this is not always accepted by user because they required modify their terminal connector even need modify their battery housing tooling. Solution two is relative simple and also has a good protection to control overcharge and thermal runaway problem. All of our G100 family models adopt solution two to protect overcharge issue. From year 2009 to now, we have not received any complains about overcharge or thermal runway defects.