The design principle of valve regulated lead-acid batteries is to inject the required amount of electrolyte into the electrode plate and separator. There is no free electrolyte, and the ability to absorb oxygen is improved by wetting the negative electrode plate. To prevent the battery from being sealed due to reduced electrolyte, valve regulated lead-acid batteries are also known as "lean battery"

When charging a battery, the internal gas recombination itself is an exothermic reaction, causing the battery temperature to rise, the floating charge current to increase, the gas evolution amount to increase, and promoting the battery temperature to rise even higher. The battery itself is a "lean liquid", tightly assembled, and difficult to dissipate internal heat. If the heat is not removed in a timely manner, it will cause thermal runaway. If the voltage at the end of float charging is too high and the ambient temperature around the battery increases, it will exacerbate the thermal runaway of the battery