Answer: The reasons are as follows:

a. Overcharge

           ① Charger float charging current is too large without timing function

           ② The charging voltage is too high after the charger parameters drift

      b, the ambient temperature is too high

      c. Single cell short circuit

      d, acid density is too high

      e. The acid error of the battery cell is too large

      f. Excessive acid absorption and quantitative deviation of the separator

      g, the plate oxidation is not the same

h, the pressure of the safety valve is not consistent

      i. The allocation is not strict

      j. Shell rupture

      k. The user privately allocates batteries into groups

It is concluded that for various reasons, water loss is serious, thermal runaway is caused, and the battery belly is deformed.