C/10 rate (amperes)
200 Ah/10 h
20 amperes.
Lead-Acid Storage Batteries
DOE-HDBK-1084-95
BATTERY COMPONENTS
AND OPERATION
Rev. 0
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Batteries
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(77ºF). The capacity is calculated by multiplying the discharge current value by the time
required to reach terminal voltage.
The most common term used to describe a battery's ability to deliver current is its rated
capacity. Manufacturers frequently specify the rated capacity of their batteries in ampere-
hours at a specific discharge rate. For example, this means that a lead-acid battery rated for
200 Ah (for a 10-hour rate) will deliver 20 amperes of current for 10 hours under standard
temperature conditions (25ºC or 77ºF). Alternatively, a discharge rate may be specified by
its charge rate or C-rate, which is expressed as a multiple of the rated capacity of the cell or
battery. For example, a battery may have a rating of 200 Ah at a C/10 discharge rate. The
discharge rate is determined by the equation below:
Battery capacity varies with the discharge rate. The higher the discharge rate, the lower the
cell capacity. Lower discharge rates result in higher capacity. Manufacturer's literature on
batteries will normally specify several discharge rates (in amperes) along with the associated
discharge time (in hours). The capacity of the battery for each of these various discharge
rates can be calculated as discussed above.
The rated capacity for lead-acid batteries is usually specified at the 8-, 10-, or 20-hour rates
(C/8, C/10, C/20). UPS batteries are rated at 8-hour capacities and telecommunications
batteries are rated at 10-hour capacities.
Series and Parallel Connections
Cells and batteries may be connected in series, parallel, or combinations of both. Cells or
batteries connected in series have the positive terminal of one cell or battery connected to
the negative terminal of another cell or battery. This has the effect of increasing the overall
voltage but the overall capacity remains the same. For example, the 12-V lead-acid
automobile battery contains 6 cells connected in series with each cell having a potential
difference of about 2 V. Another example of cells or batteries connected in series is shown
in Figure 2.
Cells or batteries connected in parallel have their like terminals connected together. The
overall voltage remains the same but the capacity is increased. For example, if two 12-V
automotive batteries were connected in parallel, the overall voltage for the batteries would
still be 12 V. However, the connected batteries would have twice the capacity of a single
12-V battery. Another example of cells or batteries connected in parallel is shown in
Figure 3.
