At S41, a present discharge electrical current and a present temperature of the battery are obtained.

At S42, a corresponding discharge cut-off voltage and a corresponding longest sustainable time duration for the battery being discharged at the discharge cut-off voltage are chosen according to the present discharge electrical current and the present temperature.

At S43, continuous discharge time durations for the battery being discharged at the discharge cut-off voltage is obtained.

At S44, a common multiple of the longest sustainable time durations corresponding to different discharge cut-off voltages in the discharge cycle of the battery, and a quotient of the common multiple and each longest sustainable time duration are calculated.

At S45, the continuous discharge time duration corresponding to each of the different discharge cut-off voltages is weighted with the quotient as a weight.

At S46, the weighted continuous discharge time durations are summed.

At S47, a summation result of the weighted continuous discharge time durations is compared with the common multiple to determine whether the summation result of the weighted continuous discharge time durations is larger than the common multiple.

If the summation result is larger than the common multiple (S47: Yes), S48 is performed. If the summation result is not larger than the common multiple (S47: No), the process returns to S43. In some embodiments, S43-S47 are repeatedly performed until the summation result becomes larger than the common multiple, and then S48 is performed.

At S48, a discharge protection is performed on the battery.