This is not marketing copy. It is an open explanation of how QZ works — written for people who understand batteries, vehicles and real-world operations: workshops, technicians and fleet managers.
The 12V battery is today the most common cause of car breakdowns — per ADAC it accounted for 45.4% of callouts in 2025, and it is the leading cause regardless of powertrain, including EVs. verified
Meanwhile modern cars save fuel with smart energy management — start-stop, charge management, regenerative braking. Battery makers themselves say these systems "place increased demands on the battery" and often leave it working in a partial state of charge. verified With an unfavourable usage profile (short trips, long standing, heavy electrical load) the battery can spend a lot of time in a state that accelerates its degradation.
QZ makes that hidden at-risk time visible and warns you when the data shows the decline, so it need not end in a car that won't start — and because it talks over 4G, it can warn you remotely, not only when you're standing next to the car.
QZ is not a workshop battery test. It does not replace a CCA / load test, real capacity (Ah) measurement, internal-resistance measurement, parasitic-draw diagnosis, or lab sulfation analysis. It is a predictive warning system, not a workshop-grade gauge. If QZ signals risk, a workshop makes the final diagnosis.
Voltage by itself is not clean proof of a battery's state — it's affected by temperature, surface charge, load, time since the last drive, battery type and the car's BMS strategy. So we do not claim "X volts = sulfation".
Instead of instantaneous voltage we work with risk-band exposure — how much time the battery spends below a healthy state of charge, corrected for temperature, driving, charging and battery type. QZ hypothesis Makers (e.g. Varta) state that when resting voltage falls below ~12.4 V the battery should be recharged as soon as possible, because sustained low charge leads to sulfation verified — but the exact risk thresholds vary by chemistry, age and temperature, so we don't present them as universal numbers until we confirm them by measurement.
The battery is not where the weather forecast is.
Into the boot of a Mercedes-AMG GT 63, where the battery sits under a double floor, we placed an independent thermometer logging every minute for eight days. At the same time we tracked the outside temperature for the car's location.
It was on average 4.2 °C warmer at the battery than outside. In the worst moments, 18 °C warmer. While it was 27 °C outside, we measured 45 at the battery. Outside temperature is not mildly inaccurate — at some moments it says nothing about the car at all.
What temperature does to a battery. Heat shortens its life — battery manufacturers state that lead-acid battery life roughly halves for every 10 °C above 25 °C. verified A battery that would otherwise last six years may not see three in a permanently overheated space. It is not a fault you could see — it is wear that happens silently.
Cold does not take its life, but its strength. At zero the battery has about four fifths of its capacity available, at minus eighteen roughly half. verified And that is exactly when the engine needs more to start, not less — cold oil puts up more resistance.
That is why the same voltage does not mean the same thing. A battery at 12.5 V in summer is roughly eighty percent charged and the car starts without trouble. The same voltage in frost means a substantially smaller reserve, and a bigger demand to start at the same time. Same number, different situation. Battery type matters too — a voltage that is perfectly fine for a conventional battery can already be below the healthy level for an AGM.
That is why QZ does not judge the voltage alone. It takes into account the temperature at the battery itself, the battery type, and how it behaved over the preceding days.
| Type | Indicative life | Cycle endurance (order of) |
|---|---|---|
| Conventional (flooded) | ~3–5 yr | ~200–300 cycles |
| EFB | 3–5 yr | ~400–600 (~2× flooded) |
| AGM | 5–8 yr | ~400–800 (~3× flooded) |
| GEL | 6–15 yr | ~800–1,200 |
These are indicative figures from technical/industry sources, not cycles-at-50%-DoD from a specific maker's datasheet — makers publish engine-start counts and relative multipliers. Real-world life depends on usage profile, temperature and state of charge. GEL is mainly a traction chemistry, rarely a car starter battery.
Operating rule: AGM is replaced by AGM, EFB by EFB, and after replacement the battery must be registered/reset in the BMS — otherwise premature failure follows. verified
An EV has no alternator; its 12V battery is charged by a DC/DC converter from the high-voltage pack. The 12V problem exists in EVs too verified, but the mechanism differs — sleep/wake modes, parasitic drain, software wake-ups — not necessarily classic sulfation for the same reason as combustion cars. So we mark QZ's EV logic as continuously validated QZ hypothesis and don't overstate it.
The QZ device (based on the Teltonika FTC880) has a low own draw in idle modes (order of a few mA, < ~1 mA in power-off sleep at 12 V, per the maker's datasheet). verified In a typical "storage" profile it is far below the standby draw of many cars; we don't state it as a fixed universal multiplier, because cars' standby draw varies.
QZ does not guarantee detection of all faults and does not replace workshop diagnostics. It is a tool that turns the invisible at-risk time of a battery into an early warning and gives a person the chance to act sooner — before a breakdown, a replacement or a tow.
Related: How to monitor your car battery remotely — without Bluetooth →