SunXtender Technical Manual

Document No. 6-0100 Rev. H
Page 18 of 43
Figure 5-8. Series/Parallel Connection for 4-Terminal Batteries (Low or High Rate Applications)
5.3 Discharging
Discharge data for Sun Xtender® AGM batteries are given in Appendix C. The capacity
delivered by the battery depends on the rate of discharge as well as the battery temperature.
The battery will deliver less capacity as the discharge rate increases and less capacity as the
temperature is lowered. Graphs are provided in Appendix C to quantify these effects. Peukert
plots (Amps vs Time) are also included, along with formulas for calculating the current that can
be removed or any discharge time from 0.5 hours to 120 hours. To calculate the discharge time
for a specified amperage, these formulas can be inverted as follows:
A = C x T
-n
T = C
1/n
x A
-1/n
(A = Amps, T = Time in hours, C & n are constants specific for each battery model)
In general, batteries should be sized such that the rated capacity is at least twice the capacity
required by the load. For example, if 100 Ah is required on average, select at least a 200Ah
battery. This approach will limit the average depth of discharge to 50% and will dramatically
extend the life of the battery (see chart of Cycle Life versus Depth of Discharge in Appendix C).