Add an EV charger to a home that already has battery storage and something subtle can go wrong. The car plugs in, the charger starts drawing seven kilowatts, and your home battery, doing exactly what it was told to do, starts emptying itself into the car.
Why your battery tries to charge your car
A home battery has one job: when the house draws power from the grid, discharge and cover it. It knows this from a small current sensor at your incoming supply. To that sensor, an EV charger is indistinguishable from a kettle or an oven. It’s all just household load.
The problem is scale. A typical EV battery is four to six times the size of a home battery. Your 13.5kWh of carefully stored cheap or solar energy disappears into the car in under two hours, and every one of those kilowatt hours has taken a round trip through two sets of electronics, losing a slice to conversion each way. The car gets charged either way; you just paid an efficiency tax and burned a battery cycle for nothing.
Route one: keep it in the family
The cleanest solution is a charger that natively understands your battery platform. Pair a Tesla Wall Connector with Powerwall and both run from one app. If you drive a Tesla, Charge on Solar then diverts surplus generation into the car while the Powerwall protects its own charge. The car and the Powerwall manage this between them, on sites with solar and no export limit. Pair a Sigenergy EV charger with SigenStor and the same intelligence applies, with the EV DC module going a step further by charging the car directly from the tower. One app, one brain, no conflicts. This is why we recommend matching the charger to the battery platform wherever possible.
Route two: the Sigen Gateway Smart Port
Running a third-party charger, a Hypervolt or a Zappi perhaps, alongside a SigenStor? The Sigen Gateway’s Smart Port is built for exactly this. Wire the charger through it and the charger becomes a managed device rather than an anonymous load: you can specify its energy source (solar surplus only, grid only, or a blend), apply load management so it never tips your main fuse over its limit, and see its consumption live and historically in the mySigen app. The battery knows precisely what the charger is doing, because the system is the one telling it what to do.
Route three: make the charger invisible
Where Smart Port wiring isn’t practical, the fallback is metering. By positioning the battery system’s current sensors so the EV charger’s circuit sits outside what the battery considers “the house”, the charger effectively disappears. The battery no longer sees charging as household demand, so it doesn’t discharge to cover it. The charger pulls from the grid (ideally on a cheap overnight window set in its own app), and your stored energy stays where it belongs.
The trade-off is intelligence: an invisible charger can’t be orchestrated. It won’t soak up solar surplus intelligently unless it has its own solar-aware CT clamp, which chargers like the Zappi provide. That’s a workable setup, but it’s two systems co-existing rather than one system co-operating.
What this means for your install
- Buying charger and battery together? Match the ecosystem. Tesla with Tesla, Sigenergy with Sigenergy. It’s the difference between co-operation and co-existence.
- Adding SigenStor to a home with an existing charger? We’ll wire it via the Smart Port where possible, bringing it under the system’s control.
- Keeping a charger that can’t integrate? We configure the metering so it’s blind to the battery, and set its schedule against your cheap-rate window.
All three routes are design decisions we make at proposal stage, not problems you should ever have to discover after installation. If you tell us what car and charger you have, or plan to have, the system arrives configured for it.
This guide is general information, not advice for your specific property. Every Powergy proposal is modelled on your actual roof, usage and tariff.