Visual home battery sizing guide

5 kWh vs 13.5 kWh vs 15 kWh Home Batteries

See how usable energy and continuous power change the backup picture using three real residential battery products rather than a generic capacity label.

Capacity and power are different: kWh tells you how much energy is stored. kW tells you how much power the battery can deliver at one time. A large battery can still be the wrong backup solution if its power output cannot support the appliances you want to run.

5 kWh class example

Enphase IQ Battery 5P

Usable capacity: 5.0 kWh
Continuous power: 3.84 kW

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13.5 kWh class example

Tesla Powerwall 3

Usable capacity: 13.5 kWh
Continuous power: 11.5 kW on-grid / 11.5 kW backup

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15 kWh class example

FranklinWH aPower 2

Usable capacity: 15 kWh
Continuous power: 10 kW

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Usable energy side by side

The bars compare the usable capacities published in the current Home Solar Atlas battery profiles. They do not include household reserve settings or conversion losses.

Enphase IQ Battery 5P

5 kWh

Tesla Powerwall 3

13.5 kWh

FranklinWH aPower 2

15 kWh

Planning runtime at different household loads

These screening examples reserve 10% of usable capacity and divide the remaining energy by a constant load. Real runtime will vary with battery reserve settings, inverter losses, temperature, state of charge, appliance cycling and whether solar is recharging the battery during the outage.

Constant load	Enphase IQ Battery 5P	Tesla Powerwall 3	FranklinWH aPower 2
0.5 kW Light essentials	9.0 hours	24.3 hours	27.0 hours
1 kW Moderate essentials	4.5 hours	12.2 hours	13.5 hours
2 kW Larger backup load	2.3 hours	6.1 hours	6.8 hours
4 kW Heavy simultaneous load	1.1 hours	3.0 hours	3.4 hours

Small modular battery

Lower kWh per unit→Add units→Scale system

Useful when the ecosystem is designed around smaller repeatable battery blocks.

Larger single battery

More kWh per unit→Longer runtime→Fewer units for the same energy target

Can simplify energy-capacity planning, but continuous and surge power still need to match the backed-up loads.

Solar + storage during an outage

Battery overnight→Daytime solar→Recharge if architecture allows

Multi-day resilience depends on daily solar production and load discipline, not battery kWh alone.

Start with the loads, not the battery brand

List the circuits and appliances you actually want during an outage.
Estimate daily kWh for those loads.
Check startup and continuous kW for HVAC, pumps and motors.
Decide whether one-night backup or multi-day solar-assisted resilience is the goal.

Run Battery Calculator How many batteries do I need?

Then compare the complete installed system

Battery price alone does not capture gateway/controller equipment, backup panel work, service upgrades, inverter compatibility, installation labor or utility program requirements.

Compare battery specs Analyze a solar quote Is a solar battery worth it?

Runtime examples are planning estimates, not guarantees. Product capacity and power values come from the current Home Solar Atlas equipment profiles and linked manufacturer sources.