BatCap: EV Battery Health

Not just Tesla: 94 EVs from 17 makes in the catalog, BYD to VW — and any other EV can be added freely. No account, no car token, no cloud. Measures in airplane mode.

Buying a used EV, or selling one, comes down to a question nobody can answer from the outside: how much of the battery is still there? BatCap works it out from something you already have in front of you at every charge — the level before, the level after, and the kilowatt hours that went in.

1. LOG THE CHARGE. One big slider for the state of charge, a stepper for the kWh, a tap for AC or DC. It takes a few seconds and you can do it with cold hands.

2. READ THE TREND, NOT THE READING. A single charge swings with temperature, with how full the pack was and with how the display rounded. So the headline is the median of your last five estimates, and the chart shows all of them against the capacity the pack had when it was new.

3. ON A FAST CHARGE, RECORD THE CURVE. Tap a button every few minutes and BatCap compares the shape against the reference curve for your model, corrected for the outside temperature. The verdict is qualitative: in the expected range, above it, or clearly below it.

Not just Tesla: 94 EVs from 17 makes come as presets, BYD to VW — and any other EV you add freely with its net capacity.

ON THE APPLE WATCH

The recording at the charger also runs from your wrist: start it, set the level, the power and the kWh with the Digital Crown, commit points, finish, with the charging curve beside them. The same recording, never a second one: the iPhone stays the truth, and the closing form opens there.

A SEALED CHARGING HISTORY, FOR THE HANDOVER

Any charge can be sealed: it can no longer be edited afterwards, and it takes its time from an independent time server. Only a checksum leaves the phone, no reading and no charging location; without a network nothing is sealed. Each seal carries the fingerprint of the one before it, so any later change breaks everything after it. The check says exactly this much: unchanged since the seal dates stated. Not that the figures were right when they were entered, and not that this history belongs to a particular car.

NO ACCOUNT, NO CAR TOKEN, NO CLOUD

Other apps here want the login to your car and then hold a token that reads your location, your trips and your charges. BatCap connects to no vehicle, and no Freshlab server holds your data. In airplane mode everything the app measures still works. No account, no analytics, no ads, no sync, no charging log anywhere but this iPhone.

THE PHOTO PATH IS OPTIONAL, THE FORM IS THE APP

If your iPhone supports Apple Intelligence, you photograph the charging screen and the on-device model fills the figures into the form. Every value it fills in is labelled as an AI suggestion until you confirm or change it — a model reading a bright screen through a windscreen gets things wrong. Nothing is saved except through the form. Without Apple Intelligence the camera button is simply not there: typing the numbers in is the full app, not a fallback.

ESTIMATES, NOT MANUFACTURER DATA

The new-capacity figures and the reference charging curves are estimates from public sources, not manufacturer specifications; BatCap is not a measuring instrument. What it gives you is an indication and a direction over time, not a warranty statement and not a number to put in a contract. A brand new pack can read above 100 %, and the app says so rather than quietly capping it.

WHAT IT COSTS

Everything measured is free, with no subscription and no monthly limit: logging charges, the trend, the chart, the curve comparison, the warranty and fleet references, sealing and the chain view. One optional one-time purchase unlocks the two handover documents: the printable battery report and the sealed charging history as a file. Checking somebody else's file, and taking a vehicle out of it, stays free and works offline. Tips are separate, voluntary, and unlock nothing.

iPhone with iOS 26; for the watch app, an Apple Watch with watchOS 26. Questions or problems: support@freshlab.es — we answer in English, Spanish and German.