5.0 APPENDIX
63
©2000 Xantrex Technology Inc.
Percent of
Full Charge
System Voltage
Individual Cell
Voltage
12 V 24 V 48 V
100% 12.7 25.4 50.8 2.12
90% 12.6 25.2 50.4 2.10
80% 12.5 25.0 50.0 2.08
70% 12.3 24.6 49.2 2.05
60% 12.2 24.4 48.8 2.03
50% 12.1 24.2 48.4 2.02
40% 12.0 24.0 48.0 2.00
30% 11.8 23.6 47.2 1.97
20% 11.7 23.4 46.8 1.95
10% 11.6 23.2 46.4 1.93
0% <
11.6 < 23.2 < 46.4 < 1.93
975-0012-019
Battery Care and Maintenance (continued)
Check Batterys State of Charge
The batterys state of charge should be checked monthly and only when the battery is not
powering heavy loads or is being actively charged. If the batteries are readily accessible,
measure the voltage across the individual battery terminals. There should be less than a 0.2 volt
difference between each battery. To determine the individual cell voltage, divide the voltage by
the number of cells in the battery (i.e., 12.6 V divided by 6 cells = 2.1 volts per cell). If a greater
difference is measured, the batteries may need to be equalized (liquid lead-acid types only) or
replaced. All batteries in the bank should measure the same voltage (this is not an accurate
measurement for cross-tied batteries as each battery is in parallel with another battery making
individual battery measurements impossible).
The voltage should match the following table for the entire battery bank output. These values
indicate the overall batterys state of charge for the entire bank. Individual cell voltages (if
available) are also shown as a percentage of charge.
The values given are for a temperature of 77 °F (25 °C). Cooler temperatures produce lower
voltage measurements.
Table 13
Battery State of Charge
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