Should I charge my EV from my home battery?
Short answer
Rarely. A 7 kW car charger can empty a 13.5 kWh battery in under two hours, and moving grid electricity through the battery into the car only adds losses. Charge the car directly on a cheap EV tariff and keep the battery for the house. The exception is free solar surplus with no cheap tariff available.
Last checked 24 September 2026 · 4 sources
What should I know before deciding?
Wire the charger so the battery does not see the car as house load (CT placement / upstream wiring) - see engineer entry. Tesla's US 'EV charging' drain-limit setting is reported as unavailable in the UK (owner forum). Some diverter-style chargers (e.g. solar-only modes) use surplus directly without passing through the battery.
Will my Powerwall drain into my electric car, and should the charger be wired before or after the battery?
It depends on where the charger sits in the wiring and how the system is set up. In a power cut Tesla only lets Powerwall charge a Tesla car down to a threshold you set, and only if the charger is on a backed-up circuit. Wiring the charger upstream of the Gateway keeps it off backup entirely.
Tesla: during an outage Powerwall charges the vehicle only above the owner's charging threshold and slows/stops it to keep the home powered; charger must be on a backed-up circuit. Partial-home backup with loads upstream of Backup Gateway 2 is a documented Tesla configuration (datasheet/owner manual figure 3). Wall Connector can be paired with Powerwall in the app; Dynamic Power Management is Gen 3 only and needs a Tesla-approved meter.
Should an EV charger be wired upstream or downstream of the battery CT?
It depends on the aim. A charger downstream of the grid CT looks like house load, so the battery may discharge into the car. Wiring it upstream, or using the inverter's EV or load-exclusion settings, stops that. Solar-diverting chargers need their own CT arrangement. Record the chosen layout and make sure export limitation still sees every path.
MIS 3012 cl.3.5.36: CT faults must not lead to export or maximum demand being exceeded. IET EV CoP applies to the charger (edition cited in MIS 3012 is outdated).
What to do next
Use your own half-hourly electricity data where possible. Compare usable kWh, kW, tariff rules and warranty terms before buying.
Sources
- teslamotorsclub.com — teslamotorsclub.com/tmc/threads/anyone-in-the-uk-got-ev-charging-option-in-powe…
- Archived page — web.archive.org/web/20250402191926/https://www.tesla.com/support/energy/powerwa…
- Archived page — web.archive.org/web/20240721105325/https://www.tesla.com/en_gb/support/charging…
- MCS — mcscertified.com/wp-content/uploads/2025/02/MIS-3012-2025-V1.0.pdf
Last checked: 24 September 2026