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How do I size my battery bank?

Sizing a battery bank for a battery based inverter/charger

Product Line:
XW/XW+, Conext SW/SW+, Schneider Electric Hybrid inverter/charger

Installations where a battery based inverter system is used (OFF Grid or ON Grid for Residential)

Calculating Battery Bank Size


Estimating Battery Requirements

Calculating Battery Size

Step 1: Compute

For each appliance, compute the number of amp-hours that will be used
between charging cycles, as follows:
1. Obtain the wattage. If the wattage is marked on the nameplate rating, use
that. Otherwise, multiply the marked voltage and amperage:
2. Obtain the Watt-hours by multiplying that amount by the hours the appliance
will be used:
3. Obtain the amp-hours that the appliance requires by dividing that amount by
20 (the factor for the Conext SW, which is a 24-volt system):

Step 2: Calculate Battery Size
Size the batteries for approximately twice the estimated total amp-hour usage.
Doubling the expected amp-hour usage ensures that the batteries will not be
overly discharged and extends battery life.
Do not skip this doubling step. More capacity is better since you will have more
reserve capacity, be better able to handle large loads and surge loads, and your
battery won’t be discharged as deeply. Battery life is largely dependent on how
deeply the battery is discharged. The deeper the discharge, the shorter the
battery life.
Troubleshooting If you find that the system shuts down when appliances with
large motors are started, the problem may be that this motor is too much for the
battery. Even though you calculated the amp-hour requirements appropriately,
the startup of a large motor makes high demands on the battery. You may find
that adding more amp-hours (in the form of extra batteries or replacement with a
bigger battery) solves the problem.

You can use the following Battery Sizing Worksheet

These steps are outlined in the Conext SW Inverter/Charger Installation guide (Rev D)

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