Samlexpower PST-15S-12A Owner's Manual page 16

Typical battery sizes
Below is a chart of some battery sizes applicable for powering inverters:
BCI * Group
27 / 31
4 D
8D
GC2**
* Battery Council International
** Golf Cart
Reduction in usable capacity at higher discharge rates.
As stated above, the rated capacity of the battery in AH is applicable at a discharge rate of
20 Hours. As the discharge rate is increased, the usable capacity reduces due to "Peukert
Effect". This relationship is not linear but is more or less according to the table below:
Table 1 Battery Capacity versus Rate of Discharge
Hours of Discharge
20
10
8
6
5
3
2
1
Using the above table will show that a 100 AH capacity battery will deliver 100% (i.e.
full 100 AH) capacity if it is slowly discharged over 20 hours at the rate of 5 Amperes.
However, if it is discharged at a rate of 50 Amperes then theoretically, it should provide
100 AH ÷ 50 = 2 hours. However, the Table above shows that for 2 hours discharge rate,
the capacity is reduced to 50% i.e. 50 AH. Therefore, at 50 Ampere discharge rate the
battery will actually last for 50 AH÷50 Amperes = 1 Hour
Battery Voltage, V
12
12
12
6
Page 15
Battery AH
105
160
225
220
Usable Capacity
100%
87%
83%
75%
70%
60%
50%
40%