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Appendix B - Batteries
Check Battery's State-of-Charge
F
B-18
The battery's state-of-charge should be checked monthly and only when the
battery is not powering heavy loads or 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 volts 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 battery's 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.
S
y
s
e t
m
P
e
c r
e
t n
f o
u
l l
C
h
a
g r
e
1
2
V
1
0
0
%
1
2
7 .
9
0
%
1
2
6 .
8
0
%
1
2
5 .
7
0
%
1
2
3 .
6
0
%
1
2
2 .
5
0
%
1
2
1 .
4
0
%
1
2
0 .
3
0
%
1
1
8 .
2
0
%
1
1
7 .
1
0
%
1
1
6 .
0
%
<
1
1
6 .
<
Table B-4
Battery State-of-Charge
V
l o
a t
g
e
n I
d
v i
d i
u
V
l o
a t
2
4
V
4
8
V
2
5
4 .
5
0
8 .
2
1 .
2
5
2 .
5
0
4 .
2
1 .
2
5
0 .
5
0
0 .
2
0 .
2
4
6 .
4
9
2 .
2
0 .
2
4
4 .
4
8
8 .
2
0 .
2
4
2 .
4
8
4 .
2
0 .
2
4
0 .
4
8
0 .
2
0 .
2
3
6 .
4
7
2 .
1
9 .
2
3
4 .
4
6
8 .
1
9 .
2
3
2 .
4
6
4 .
1
9 .
2
3
2 .
<
4
6
4 .
<
1
©2002 Xantrex Technology Inc. All Rights Reserved.
l a
C
e
l l
g
e
2
0
8
5
3
2
0
7
5
3
9 .
3
P/N 975-0026-01-01 Rev A 06/2002
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