Battery Backup Sizing Calculator

Estimate how much battery capacity you need to back up your home and compare costs across popular residential battery systems. Choose whole-home, essential-loads, or solar-plus-storage mode to see the right sizing for your situation.

Daily Energy Usage (kWh)

Backup Hours Desired

Depth of Discharge (%)

Round-Trip Efficiency (%)

Pricing (edit to match local rates)

Powerwall ($/unit)

Enphase IQ 5P ($/unit)

LG RESU Prime ($/unit)

Generac PWRcell ($/unit)

Usable Capacity Needed

33.3 kWh

30.0 kWh/day for 24h

Total Battery Capacity

41.7 kWh

Accounting for 80% DoD & 90% efficiency

Best Value

Generac PWRcell

3 units · $30,000.00

Purchase Option	Quantity	Est. Cost
Tesla Powerwall	4 units	$46,000.00
Enphase IQ 5P	9 units	$49,500.00
LG RESU Prime	3 units	$36,000.00
Generac PWRcellBest value	3 units	$30,000.00

Cheapest option: Generac PWRcell at $30,000.00Whole-home backup requires 41.7 kWh of total battery capacity. Consider whether all loads truly need backup — switching to essential loads only could reduce your battery requirement by roughly 60%.

Generac PWRcell ScalabilityThe Generac PWRcell uses a modular battery cabinet (9–18 kWh per unit). Confirm with your installer whether you need the base 9 kWh configuration or the fully populated 18 kWh cabinet — the price above assumes the full 18 kWh configuration.

This is an estimate for planning purposes. Actual battery performance varies with temperature, load profile, battery age, and installation configuration. Always consult a certified electrician or solar installer for final system design.