Battery manufacturers recommend that new batteries be slow-charged for 16 to 24 hours before use. A slow charge brings all cells in a battery pack to an equal charge level. This is important because each cell within the nickel-cadmium battery may have self-discharged at its own rate. Furthermore, during long storage the electrolyte tends to gravitate to the bottom of the cell and the initial trickle charge helps redistribute the electrolyte to eliminate dry spots on the separator.
Stationary batteries are almost exclusively lead acid and some maintenance is required, one of which is equalizing charge. Applying an equalizing charge every six months or after 20 cycles brings all cells to similar levels by increasing the voltage to 2.50V/cell, or 10 percent higher than the recommended charge voltage.
With technical knowledge, batteries can be charged manually with a power supply featuring user-adjustable voltage and current limiting. I stress manual because charging cannot be left unattended; charge termination is not automated. You need to observe the state-of-charge according to voltage and current behaviors. Lower the charge voltage or disconnect the charge when the battery is full. Because of difficulties in detecting full charge with nickel-based batteries, I recommend only charging lead acid and Li-ion batteries manually.
We now study various charging methods and examine why some systems work better than others. We focus on closed-loop techniques that communicate with the battery and terminate charge when certain responses occur.