A car that sits won't tell you it's in trouble. You usually find out about a weak battery when you're standing next to it and it won't start. You can know earlier — and from anywhere.
A weak 12V battery is, per ADAC, the most common cause of car breakdowns — 45.4% of callouts in 2025, regardless of powertrain. For a car that isn't driven every day, several things add up:
The result: after a few weeks of standing the voltage can be in a zone where a start is no longer certain — and you can't see it from the outside.
A charger and QZ aren't rivals. The charger tops the battery up; QZ tells you the truth about its state and warns you when it's time to act — even when you're not at the car.
The difference isn't that it "measures voltage" — a cheap voltmeter does that too. The difference is that you find out, anywhere and in time. QZ talks over the cellular network (4G LTE is included in the device price, with no Wi-Fi and no phone pairing), so you don't need to be at the car or have internet in the garage.
QZ doesn't just watch the instantaneous voltage — it watches the battery's behaviour over time: how fast it drops, how it recovers, how long it spends in a risk band, in the context of temperature and battery type. When the state worsens, it warns you before a quiet decline becomes a car that won't start. QZ won't charge the battery for you — it gives you time to act (charge, a longer drive, a workshop). Exactly what and how we measure is described in the QZ Methodology.