C. Equalizing Charge
C. Equalizing Charge
The purpose of the equalizing charge is to ensure that every plate in every
cell is brought with certainty to a state of full charge by a slight overcharge.
Do not perform equalizing charges on a routine basis. If one of the conditions below
occurs, apply an equalizing charge at the voltage recommended by the
manufacturer for the type of cell. Ensure that all cell levels are at the high
level mark before beginning the charge.
1. Following heavy discharge.
2. If specific gravity (corrected for temperature) of any cell is more than 10
points (0.010) below the full charge value while on float.
3. If the voltage of any cell is more than 0.04 volt below the average cell
voltage when the battery is on float.
4. If the level in any cell or cells falls at or near the minimum fill line a lot
of distilled water must be added to restore the level to the maximum fill
line. If this condition occurs, an equalizing charge must be performed to
restore specific gravity.
5. If too little replacement water is being added, typically indicating
undercharging (see fig. 1 for typical water consumption).
Terminate the equalizing charge when all conditions below are met:
1. Every cell gasses freely and equally.
The specific gravity of all low cells has stopped rising, determined by two
specific gravity readings measured over the last one-eighth of the
3. The voltage difference between the highest and lowest cells is no greater
than at the initial charge.
Failure to give equalizing charges when needed leads to problems. The
ampere-hour capacity of weak cells greatly decreases. During discharge,
these cells will be exhausted well ahead of good cells and then become over
discharged (see section 2.11) or over sulfated; the plates may buckle, and
grids may crack. Continued discharge may reverse the polarity, making
positive plates out of the negatives and vice versa, which will destroy the
If one section of the battery runs warmer than the rest, these cells have a
higher rate of internal self-discharge, and capacity gradually falls below the
others. Hence, a battery must be located so that sunshine or space heaters
do not affect a portion of the battery, which would mask internal self