Depth of discharge and battery life
The more deeply a battery is discharged on each cycle, the shorter the battery life.
Using more batteries than the minimum required will result in longer life for the
battery bank. A typical cycle life chart is given at Table 2 below:
TABLE 2. – TYPICAL CYCLE LIFE CHART
Depth of Discharge
Cycle Life Cycle Life Cycle Life
% of AH Capacity
Group 27 / 31
Group 8D Group GC2
10
1000
1500
3800
50
320
480
1100
80
200
300
675
100
150
225
550
It is recommended that the depth of discharge should be limited to 50 %
Loss of battery capacity at low temperatures
Batteries lose capacity in low temperatures. At 32 º F, a battery will deliver about 70 to
80 % of its rated capacity at 80 º F. If the air temperature near the battery bank is
lower than 80 º F, additional batteries will be needed to provide the same usable
capacity. For very cold climates, an insulated / heated battery compartment is
recommended.
Series and parallel connection of batteries
When two or more batteries are
connected in series
, their voltages add up but their
AH capacity remains the same. For example, when two 12 V, 105 AH batteries are
connected in series, it becomes a 24 V, 105 AH battery. (Positive of the first battery
is the positive terminal of the series connection. The negative of the first battery is
connected to the positive of the second battery. The negative of the second battery is
the negative of the series connection)
When two or more batteries are
connected in parallel
, their voltages remain the
same but their capacities add up. For example, if two 12 V, 105 AH batteries are
connected in parallel, their voltage remains 12 V but their capacity becomes 105 × 2
= 210 AH (Connect the positive terminal of the first battery to the positive terminal
of the second battery. These paralleled common positive terminals become the
positive terminal of the parallel combination. Connect the negative terminal of the
first battery to the negative terminal of the second battery. These paralleled common
negative terminals becomes the negative terminal of the parallel combination)
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