Round-trip efficiency is the percentage of the energy stored in a battery that comes back out when it discharges; the rest is lost as heat in charging, conversion and storage. It matters most when a battery is used every day to shift solar into the evening, because every cycle loses that share of the stored energy. Manufacturers measure it under different conditions, for example from solar to battery to home, or at the battery terminals, so compare figures from datasheets with care. Usable capacity, continuous power output and the warranty's throughput or retention terms matter as much as efficiency when you compare batteries.
Related terms and pages
- Time-of-use rate: An electricity rate whose price per kWh depends on the hour, highest in the evening peak.
- Net billing: Billing in which exported solar is credited at a rate below what you pay for power.
- Home batteries compared