Xantrex PRO XM 1000 Owner's Manual page 64

Battery Reserve
Capacity
Amp-hour (Ah)
Capacity
975-0263-01-01
Battery reserve capacity is a measure of how long a battery can deliver a
certain amount of current—usually 25 amps. For example, a battery with
a reserve capacity of 180 minutes can deliver 25 amps for 180 minutes
before it is completely discharged.
Amp-hour capacity is a measure of how many amps a battery can deliver
for a specified length of time—usually 20 hours. For example, a typical
marine or RV battery rated for 100 Ah can deliver 5 amps for 20 hours
(5 A × 20 hours = 100 Ah).
This same battery can deliver a higher or lower current for less or more
time, limited approximately by the 100 Ah figure (for example, 50 A for 2
hours, or 200 A for 1/2 hour), but usually the capacity figure given is only
accurate at the specified rate (20 hours).
To calculate the battery capacity you require, read "Estimating Battery
Requirements" on page B–4 and "Battery Sizing Example" on page B–4,
and then complete the "Battery Sizing Worksheet" on page B–5.
Battery Size
B–3