Powerwall 3
IQ Battery 5P
aPower 2
See the capacity difference visually
Before using the unit-count tables below, open the 5 kWh vs 13.5 kWh vs 15 kWh visual comparison for capacity bars and simple runtime examples at several constant household loads.
Powerwall 3
13.5 kWh usable · 11.5 kW on-grid / 11.5 kW backup
IQ Battery 5P
5.0 kWh usable · 3.84 kW
aPower 2
15 kWh usable · 10 kW
Battery units needed for one day of backup
This energy-only table keeps a 10% planning reserve and assumes no solar recharge during the outage. It uses the manufacturer-published usable capacity in the Home Solar Atlas battery catalog. Round-up is intentional because a fraction of a battery unit is not installable.
| Daily backup energy | Tesla Powerwall 3 | Enphase IQ Battery 5P | FranklinWH aPower 2 |
|---|---|---|---|
| 5 kWh/day | 1 unit | 2 units | 1 unit |
| 10 kWh/day | 1 unit | 3 units | 1 unit |
| 15 kWh/day | 2 units | 4 units | 2 units |
| 20 kWh/day | 2 units | 5 units | 2 units |
| 30 kWh/day | 3 units | 7 units | 3 units |
Simplified runtime from one battery unit
These hours are capacity divided by a constant load with the same 10% planning reserve. They do not model inverter losses, temperature, battery controls, changing household demand or solar recharge.
| Constant backed-up load | Tesla Powerwall 3 | Enphase IQ Battery 5P | FranklinWH aPower 2 |
|---|---|---|---|
| 0.5 kW | 24.3 hours | 9.0 hours | 27.0 hours |
| 1.0 kW | 12.2 hours | 4.5 hours | 13.5 hours |
| 2.0 kW | 6.1 hours | 2.3 hours | 6.8 hours |
Energy capacity is only half of battery sizing
A battery bank can have enough kWh for a full day and still be unable to start or run every appliance you want. Continuous output and short-duration surge capability must be checked separately.
- Refrigerators, lights, internet equipment and electronics usually create a much smaller backup load than whole-home HVAC.
- Air conditioners, well pumps and other motors can require a large startup surge even if their average energy use is manageable.
- Electric resistance heating, electric water heating, ovens and EV charging can consume battery energy very quickly.
- Whole-home backup may also require a gateway, system controller, load-management hardware or electrical upgrades.
A better way to choose battery capacity
- List the circuits or appliances you actually need during an outage.
- Estimate their daily energy in kWh and their highest simultaneous power in kW.
- Decide how many hours or days of no-solar backup you want to plan for.
- Check whether daytime solar can recharge the battery during a grid outage in the proposed system architecture.
- Compare manufacturer power, capacity, warranty and expansion limits before choosing a final design.
Specification sources
Battery capacities and power ratings are pulled from the current Home Solar Atlas equipment catalog, which links to official manufacturer product pages and records a verification date for each model.