Capacity is only half of backup sizing
A battery can have enough stored energy for several hours but still lack enough instantaneous power for simultaneous HVAC, pumps or other heavy loads. This tool checks both requirements. For a simpler visual explanation first, open the home battery capacity comparison.
Estimate battery count for your backup target
Set an average backed-up load and desired runtime. The estimate checks both stored energy and continuous power, then uses whichever requires more full battery units.
Screening estimate only. Real backup design must account for starting surge, load profiles, reserve settings, temperature, conversion losses, code requirements and manufacturer-specific configuration limits.
Choose 2-3 batteries
All three are selected by default.
Estimated full battery units
The calculator does not treat add-on expansion packs as equivalent to another complete battery unit.
Powerwall 3
Large 13.5 kWh unit with high 11.5 kW continuous output and an integrated solar inverter.
Open full Powerwall 3 profile →
IQ Battery 5P
A 5 kWh modular AC-coupled building block that integrates tightly with the Enphase Energy System.
Open full IQ Battery 5P profile →
aPower 2
A 15 kWh AC-coupled battery with 10 kW continuous output and a long published scalability range.
Open full aPower 2 profile →What matters most to you?
This changes the homeowner context, not the manufacturer specifications.
Large 13.5 kWh unit with high 11.5 kW continuous output and an integrated solar inverter.
A 5 kWh modular AC-coupled building block that integrates tightly with the Enphase Energy System.
A 15 kWh AC-coupled battery with 10 kW continuous output and a long published scalability range.
Side-by-side specifications
| Specification | Tesla Powerwall 3 | Enphase IQ Battery 5P | FranklinWH aPower 2 |
|---|---|---|---|
| Usable capacity | 13.5 kWh | 5.0 kWh | 15 kWh |
| Continuous power | 11.5 kW on-grid / 11.5 kW backup | 3.84 kW | 10 kW |
| Peak / surge | Motor-start capability rated to 185 LRA | 7.68 kW for 3 seconds; 6.14 kW for 10 seconds | 15 kW for 10 seconds |
| Chemistry | See Tesla current technical documentation | See current Enphase datasheet | Lithium iron phosphate (LFP) |
| Coupling / architecture | Integrated solar inverter; can also be added to existing solar | AC-coupled with six embedded grid-forming microinverters | AC-coupled |
| Warranty | 10-year limited warranty | 15-year limited warranty, up to 6,000 cycles | 15 years or 60 MWh throughput |
| Scalability | Expansion available; up to 40.5 kWh additional energy capacity per Powerwall 3 unit | Modular system design | Up to 225 kWh / 15 units per aGate |
Use this as a screening tool, not an electrical design
The runtime estimate uses average load × desired hours and compares that result with each product's published usable capacity and continuous output. It does not model appliance start-up sequences, reserve state of charge, conversion losses, temperature derating, utility rules or installer-specific hardware.
Product specifications were last checked against manufacturer sources on August 27, 2026. Verify current compatibility, expansion options, backup controls and warranty documents before purchase.