BATTERY AMPERE/HOUR CAPACITY

For battery back up systems, ampere/hour capacity is the important rating to know. This rating is based on the total number of amperes the battery can supply in a 20 hour period of even withdrawal. Accordingly, a battery rated at 100 ampere/hours can supply 5 amperes per hour for 20 hours. If more than 5 amperes per hour is taken from the battery, it will not even supply its 100 ampere/hour rating.

Other factors, which reduce the available ampere/hours, are battery age, ambient low temperature, and state of charge. Considering some or all of these factors, we rarely have 100% of a battery’s rated capacity available. To compensate, we should consider only 75% of the rated capacity to be available.

Quantity

Voltage

Group
Size

Ah Rating

75% Of
Max*

Amps Per
Hour

One

12 Volt

24

40 – 85

64 Amps

2 – 4

One

12 Volt

27

85 – 105

80 Amps

4 – 5

One

12 Volt

4 D

140 – 160

120 Amps

7 – 8

One

12 Volt

8 D

200 – 215

160 Amps

10 – 11

Two

6 Volt

T-105

200 – 225

170 Amps

10 – 11

Two

6 Volt

L-16

325 – 350

260 Amps

16 – 17

Four

6 Volt

T-105

400 – 450

340 Amps

20 - 22