Maintainer or QZ

Battery maintainer or QZ? When a charger is enough, when monitoring is — and when you want both

The short answer: if the car sits in a garage with a socket and you are nearby, a battery maintainer is the cheaper and better choice. QZ is worth it where a charger can't reach — or when you want to know whether it is really charging.

What a maintainer does and what QZ does

	Battery maintainer	QZ
Charges the battery	yes	no — it measures and alerts
Needs a socket	yes	no, it runs off the battery
Where you see the state	at the car; some models in an app over Bluetooth when you are close	on your phone from anywhere, over 4G
Speaks up on its own	no	yes, when the data shows growing risk
Draw from the battery	—	about 6 mA, ≈ 0.14 Ah a day
Price	one-off, typically tens of euros	199 € including the first year, then 49 €/year

Real measurements

Battery voltage at night (2:00 – 5:00, vehicle parked) — measured directly at the battery every 10 minutes. Only nights with a clean reading are shown.

The founder's motorcycle, 18 days parked — GEL 14 Ah

The voltage fell from 12.73 V to 12.48 V — steadily, about 14 mV a day. On a battery this small, QZ itself is a real part of the draw: about 6 mA, roughly 1 % of the capacity a day. Verdict: a motorcycle that stands over winter belongs on a maintainer. QZ does not replace it — it can only remind you in time that it is time to plug it in.

The founder's car, six weeks of normal use — Mercedes-AMG GT 63, AGM 92 Ah

The car is driven irregularly. On parked days the voltage falls by 2 to 5 hundredths of a volt a day and a drive brings it back. On 13–14 September it was on a charger (13.30 V at night). On 25 August, during a workshop visit, it dropped to 12.27 V — well below this battery's healthy band. Verdict: a car that is driven regularly does not need a maintainer. QZ shows whether the drives really recharge the battery, and speaks up when they don't.

Which one when

The car sits in a garage with a socket and you are nearbyA maintainer. It is cheaper and actually charges the battery. You don't need QZ here.

A motorcycle or a small battery over winterA maintainer. A small battery has no reserve, and QZ itself would take a noticeable share of it.

The car sits without a socket, outdoors, at another address, or is driven irregularlyQZ. A charger can't be plugged in there. QZ measures all the time and speaks up when the data shows growing risk — while there is time to act.

A rare or seasonal car on a maintainer that you don't see every dayBoth. The maintainer charges, QZ shows whether it really does. If the plug or a breaker trips, the voltage starts to fall as in normal parking — you see it in the app, and QZ alerts you when it drops below the healthy limit.

What to watch with a maintainer

Pick the mode for your battery type — AGM, EFB and LiFePO4 need different charging from a regular lead-acid battery.
Connect it as the car's manual says. Some cars have charging points under the bonnet and the battery elsewhere.
Check now and then that it shows it is charging. A charger that quietly stopped is worse than none — you rely on it.

To be clear: QZ does not charge and does not measure capacity or cranking current — a workshop tester does that. QZ follows how the battery behaves in real life and alerts you when it is getting worse.

How QZ works →

Car won't start after sitting? Why, and what to do →

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