EV chargingkWh mathsizinglevel 2load shifting

Can a home battery charge an EV? The kWh math

Electrically yes, and the arithmetic is unforgiving. The largest home battery we track holds under a fifth of the smallest F-150 Lightning pack, and a Level 2 charger at full draw exceeds the entire continuous output of 14 of the 16 models we track.

The Home Battery ReportAugust 6, 20269 min read✓ Verified

The question arrives in two forms. One is whether a home battery can charge an electric car at all, which has a boring yes for an answer. The other is whether a home battery is a sensible way to charge an electric car, which is arithmetic, and the arithmetic is one-sided.

This guide runs it on published figures only: usable capacity from the datasheets behind the 17 models we track, EV pack sizes from a manufacturer that publishes them, and charger draw from the charger makers' own specifications. There are no dollar figures anywhere on this page, because none of the numbers below are prices and we do not invent them.

The mechanic, which is simpler than people expect

A home battery does not charge a car. It powers your electrical panel, and the charger on that panel draws from whatever is feeding it. There is no EV mode in any of the datasheets we read, no handshake between battery and vehicle, and no way for the charger to know the difference between grid electrons and battery electrons.

That has one useful consequence and one uncomfortable one. The useful one is that any home battery capable of backing up a circuit can technically charge a car on that circuit. The uncomfortable one is that the charger is just a very large appliance, competing with the refrigerator, the well pump and everything else for the same continuous kilowatts. If the battery is carrying the house during an outage, every kilowatt going to the car is a kilowatt not going to the house.

How the capacities compare

Ford is the useful comparison here, because Ford publishes usable pack energy rather than a nominal figure. Its 2025 F-150 Lightning technical specifications list three packs, each stated as usable energy: 98 kWh standard range, 123 kWh extended range, and 131 kWh extended range, against EPA-estimated ranges of 240, 300 and 320 miles respectively.

Now the home side. Usable capacity as each maker's datasheet publishes it, for the models we track:

Fortress Power eVault Max 18.5: 18.43 kWh, the largest usable capacity among the models we track, rated at 100 percent depth of discharge.
Panasonic EverVolt 2.0, Qcells Q.HOME CORE and Generac PWRcell: up to 18 kWh in the largest cabinet configuration.
Savant Power Storage 20: 18 kWh, our figure derived from the datasheet's 20 kWh rated capacity at its published 90 percent recommended depth of discharge.
FranklinWH aPower 2: 15 kWh.
EG4 PowerPro WallMount: 14.3 kWh.
LG Home 8: 14.4 kWh usable out of 15.8 kWh total.
Tesla Powerwall 3 and Powerwall 2: 13.5 kWh. The Powerwall 2 is discontinued.
SunPower SunVault: 12 kWh. Discontinued.
BYD Battery-Box Premium HVS: 10.24 kWh in the four-module HVS 10.2 configuration.
Enphase IQ Battery 10C and sonnen sonnenCore+: 10 kWh.
SolarEdge Home Battery 400V: 9.7 kWh at 100 percent depth of discharge.
Enphase IQ Battery 5P: 5 kWh.
Anker SOLIX X1: not published. Anker publishes 10, 15 or 20 kWh nominal per configuration and no usable figure, so there is no usable number for us to print.

Put the two sides together, with the arithmetic labelled as ours:

A full Tesla Powerwall 3 at 13.5 kWh emptied entirely into a 98 kWh Lightning pack covers about 14 percent of it.
The largest single unit we track, 18.43 kWh, into that same 98 kWh pack covers about 19 percent. Into the 131 kWh pack, about 14 percent.
The smallest, 5 kWh, into the 131 kWh pack covers about 4 percent.

Not one of those numbers is close. A residential storage battery is roughly a seventh of a full-size electric truck's pack, and that is before you account for the fact that emptying a home battery into a car leaves the house with nothing. The comparison is not close enough for a bigger model or a second cabinet to change the conclusion.

The charger is larger than most of these batteries

Capacity says how much. The second constraint is how fast, and it is the one people miss.

What a Level 2 charger draws. Tesla states its Wall Connector "can provide up to 11.5 kW / 48 amp output," and the Gen 3 Wall Connector manual publishes a current output range of 12 to 48 amps at a nominal 200 to 240 V AC single phase. Ford's spec sheet lists an onboard charger drawing 11.3 kW at the input and delivering 10.5 kW at 48 A on all three packs, with a dual onboard charging option at 19.2 kW input and 17.6 kW output that Ford marks fleet only. Ford's 80 A Charge Station Pro and its 30 A mobile charger sit either side of that.

What the batteries publish as continuous output. Of the 16 models we track with a published continuous figure, exactly two match or exceed 11.5 kW: the Savant Power Storage 20 at 12.5 kW and the Tesla Powerwall 3 at 11.5 kW. The next rung down is the Generac PWRcell at 10.5 kW in its six-module configuration, then the EG4 PowerPro at 10.2 kW and the FranklinWH aPower 2 at 10 kW. At the other end, the Enphase IQ Battery 5P publishes 3.84 kVA and the sonnen sonnenCore+ 4.8 kW, both of which a single Level 2 charger at full output would overrun on its own. The full column, and why kW and kVA are not interchangeable, is in our continuous versus peak power guide.

So on a Powerwall 3, an 11.5 kW charger at full draw is the entire unit. The battery's 13.5 kWh divided by 11.5 kW is roughly 70 minutes of flat-out discharge, with nothing left over for the house and nothing meaningful added to the car.

The fix is not a larger battery. It is amperage: most Level 2 chargers let you set a lower current limit, and dropping a charger to 16 or 24 A turns it from an impossible load into an ordinary one. That is a setting, not a purchase.

What a full battery is worth in miles

Convert the capacity into the unit people actually think in, using Ford's own published pairing and labelling the assumption.

Ford publishes 20 miles of range per hour of charging on the 48 A Connected Charge Station, for all three packs, and separately publishes an onboard charger input of 11.3 kW. Taken together, roughly 11.3 kWh at the wall buys about 20 miles, which is our arithmetic on Ford's two figures rather than a figure Ford states in kWh per mile.

On that basis:

A 13.5 kWh Powerwall, discharged completely, is in the neighborhood of 24 miles.
The 18.43 kWh eVault Max is around 32 miles.
The 5 kWh IQ Battery 5P is around 9 miles.

Every one of those is optimistic. It ignores the battery's own round-trip losses, ignores the house continuing to consume power, and ignores that no manufacturer recommends running a battery to zero. Ford's slowest published option, the 30 A mobile charger at 240 V, delivers 13 miles per hour and takes 15 to 20 hours to go from 15 to 100 percent depending on pack, which is a useful reminder of how large these packs are relative to any residential source.

Twenty-odd miles is not nothing. It is a trip to a hospital, a shelter, or a working charger. It is not a commute week.

The losses, stated plainly

Charging a car through a home battery adds a conversion the grid does not require.

The models we track that publish a full AC round trip with stated conditions cluster around 90 percent, though the wider table runs from 85.4 to 98 percent on figures measured on different bases: Enphase publishes 90 percent AC to battery to AC at 50 percent power rating on both IQ batteries, FranklinWH publishes 90 percent grid to battery to load, LG publishes greater than 90 percent, Anker publishes up to 90.2 percent measured AC to battery to AC at 77 degrees Fahrenheit, and Savant publishes 93.8 percent. Tesla's Powerwall 3 figure of 89 percent is a solar round trip, solar to battery to home and grid, footnoted as a typical solar shifting use case, so it is not comparable to the AC-to-AC figures above it and we flag that wherever efficiency is compared.

At 90 percent, delivering 1 kWh to the charger costs about 1.11 kWh into the battery. Then the charger and the vehicle's onboard charger take their own cut. Charging directly from the grid skips all of it.

Which means the efficiency argument for routing EV charging through a home battery does not exist. The argument, if there is one, has to be about timing or about outages. That is covered next.

The two patterns the arithmetic does support

Outage top-ups. During a grid outage, a partial charge is worth far more than its size suggests, because the alternative is a car that cannot move. Twenty-odd miles from a full battery, or less from a battery that is also running the refrigerator, reaches most destinations that matter in an emergency. The honest version of this is a reserve, not a range extender, and it competes directly with the house loads for the same kilowatt-hours. Note also that several vehicles run this flow in the opposite direction: Ford publishes Intelligent Backup Power on the Charge Station Pro and a 9.6 kW Pro Power Onboard option with a 240 V outlet in the bed, which is the truck backing up the house rather than the house charging the truck.

Time-of-use shifting. This is the case that actually holds up, and it is not really about the car. On a time-of-use rate, the battery charges during the cheap window and discharges during the expensive one, so the kilowatt-hours your house consumes at peak were purchased off peak. An EV charger is simply the largest load in the house, which makes it the load where the timing matters most. The formula, the breakeven condition, and two worked examples on real published tariffs are in our load shifting guide, and how the underlying capacity arithmetic works is in kWh explained. Note the simpler alternative before you buy hardware for this: scheduling the charger itself to run off peak achieves the same timing shift with no battery, no conversion losses, and no throughput consumed.

What to check before you plan around this

Your charger's adjustable current setting, which is the difference between a load your battery can carry and one it cannot.

Your battery's continuous output, against the charger draw you actually intend to use rather than the charger's maximum.

Your warranty's throughput or cycle cap, because energy routed to a car passes through the battery and consumes the allowance either way. Generac's PWRcell module warranty is 10 years or 7.56 MWh per module. FranklinWH's aPower 2 is 15 years or 60 MWh. Anker publishes aggregate throughput figures of 32.9, 49.4 and 65.8 MWh across the three SOLIX X1 capacities. Which limit binds first for your usage is the subject of our degradation guide.

Whether your manufacturer classifies EV charging inside its uncapped warranty bucket. Tesla's Powerwall warranty grants unlimited cycles for solar self-consumption, time-based control and backup, and caps everything else at 37.8 MWh. We are not going to tell you which side EV charging lands on, because that is Tesla's determination and not a published one. Ask for it in writing.

Every figure on this page comes from a manufacturer's published specification, quoted with the basis that maker states, and the conversions to percentages and miles are our own arithmetic on those figures, labelled as such. We have not tested any of these products. Your own vehicle's pack, your charger's setting and your house's simultaneous load are the numbers that govern, and none of them are on a datasheet we can read for you.

Frequently asked questions

Can a home battery charge an electric car?

Yes, in the sense that the battery powers your electrical panel and the charger is a load on that panel. There is no special EV mode involved: the battery discharges to the house, the charger draws from the house, and it cannot tell the difference. What it cannot do is fill the car. Tesla's Powerwall 3 holds 13.5 kWh usable. Ford publishes 98 kWh of usable energy in the standard-range F-150 Lightning pack. A full Powerwall emptied entirely into that truck moves it about 14 percent of the way, by our arithmetic on both published figures, before any conversion losses.

How many miles does a home battery add to an EV?

Ford publishes 20 miles of range per hour of charging on its 48 A Connected Charge Station across all three F-150 Lightning packs, and an onboard charger that draws 11.3 kW at the input. By our arithmetic on those two figures, roughly 11.3 kWh at the wall buys about 20 miles. A 13.5 kWh home battery discharged completely into that pairing is therefore in the neighborhood of 24 miles, before round-trip losses on the battery side and before anything else in the house draws a watt. Your car, charger and conditions will differ.

Is a Level 2 charger too much for a home battery to run?

For most models, at full draw, yes. A Tesla Wall Connector provides up to 11.5 kW at 48 A. Of the 16 models we track that publish a continuous power figure, only two match or beat that: the Savant Power Storage 20 at 12.5 kW and the Tesla Powerwall 3 at 11.5 kW. The other 14 are below it, several by a wide margin, so a charger at full output would consume the battery's entire capability with nothing left for the refrigerator. Most EV chargers can be set to a lower amperage, and that is the practical answer, not a bigger battery.

Should I buy a home battery to charge my EV?

We would not frame the purchase that way, because the capacity ratio does not support it. A battery large enough to fill an EV pack does not exist in the residential market, and the largest usable capacity among the models we track is 18.43 kWh on the Fortress Power eVault Max 18.5. The two patterns the arithmetic does support are an outage top-up, where a partial charge is the difference between stranded and mobile, and time-of-use shifting, where the battery changes when grid energy was purchased rather than replacing it.

Does charging an EV from a home battery waste energy?

It adds a conversion the grid did not require. Manufacturers publish AC round-trip efficiencies around 90 percent for the models we track, so about 1.11 kWh has to go into the battery for every 1 kWh that comes back out, before the EV charger and the car's own onboard charger take their share. Charging the car directly from the grid skips the battery's conversion entirely. That does not make the battery route wrong, it just means the reason has to be timing or outage readiness rather than efficiency.

Does EV charging count against my battery warranty?

It consumes whatever throughput or cycle allowance your warranty carries, since the energy passes through the battery either way. Whether it changes which warranty bucket you are in is a separate question worth asking in writing. Tesla's Powerwall warranty grants unlimited cycles for solar self-consumption, time-based control and backup, and caps coverage at 37.8 MWh of throughput for applications outside that list. Ask your manufacturer to confirm in writing how it classifies EV charging before you plan on doing it daily.