Page 127 - Lindens Handbook of Batteries

5.4 PRINCIPLES OF OPERATION

(b)
FIGURE 5.3 Battery pack terminal design options.

4. Additional protection methods. Protection methods go beyond external mechanisms. Proper bat-
tery pack assembly is also critical to preventing internal short circuits within the battery pack (see
Sec. 5.4).

5.2.3 Voltage Reversal

Due to variability in manufacturing, capacities will vary from battery to battery. When discharged in
a series configuration, the capacity of the weakest cell in the series string of a multicell battery will
be depleted before the others. If the discharge is continued, the voltage of the low-capacity cell will
reach 0 V and then reverse. The heat generated may eventually cause pressure buildup in the cell and
subsequent venting or rupture. This process is sometimes referred to as “forced discharge.”
A common test to determine the ability of cells to withstand voltage reversal is the forced-discharge
test. The cells are deliberately discharged, at specified currents, to below 0 V by other cells in a series
string or by an external power supply to determine whether a venting, rupture, or other undesired
safety problem arises.