A home battery stores electrical energy and later supplies electricity. A heat battery stores thermal energy and later supplies heat. Solar and cheap tariffs can charge either, but the useful outputs differ.
The short answer
Store electricity when later demand includes appliances, lighting or export and the electrical system supports it. Store heat directly when the later demand is definitely hot water or space heating and the thermal path is cheaper or more compact.
Conversion route
Electricity stored in a home battery can later run an immersion or heat pump, passing through two conversion stages. Direct thermal charging may be simpler for a known heat load, but cannot turn back into household electricity.
Capacity is not comparable by the label
Both may quote kWh, yet one is electrical output and the other thermal output. Include inverter efficiency, heating efficiency and standing loss along the complete route.
Backup power
A heat battery does not normally power sockets during an outage. A home battery only provides backup when the installation includes appropriate islanding and protected circuits.
Solar priority
One surplus kWh cannot charge both. Controls should decide whether electricity serves immediate loads, electrical storage, thermal storage, an EV or export.
Value of flexibility
Electrical storage has more possible outputs; thermal storage may offer a lower-cost or space-efficient answer to one large heat load. Price the job, not flexibility in the abstract.
Your next step
List the evening loads you want to serve in kWh, divided into heat and electricity. Compare storage routes against that real split.
Sources
Primary and independent references checked by our editorial team.
- Energy storage options explained — Energy Saving Trust Checked 10 Nov 2026