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Battery Saver

Battery Saver (Pro) looks after the battery the heater runs on. It warns when the battery runs low, and stops the heater before it runs the battery flat. You set the levels; the app only recommends some.

Your settings

  • Warn below: a notification when the battery stays below this level while the heater runs. Once per run.
  • Stop below: the heater is stopped when the battery stays below this level. It cools down normally; nothing cuts its power.
  • Must stay low for: 1, 2 or 5 minutes (2 by default). A dip shorter than that never counts.

Each level has its own switch, so you can have warnings without a stop, or a stop without warnings. One of them stays on; to turn Battery Saver off, use its main switch. With both on, the warning sits at least 0.2 V above the stop.

  • Lead-acid / AGM: warn below 12.0 V, stop below 11.6 V.
  • Lithium (LiFePO4): warn below 12.2 V, stop below 11.8 V. Its voltage stays flat until it is nearly empty, then falls fast.

Tap Use to fill in either pair, then adjust them to suit you. Your battery maker's advice comes first.

Check what your heater reads. Heaters read the voltage at their own terminals, often a few tenths below the battery's own monitor, and lower still at full power. With a charged battery, run the heater at Power Level 10 for a few minutes and look at the reading on this card. Keep your warning level at least 0.2 V below it, or the warning comes on a healthy battery.

A 24 V system doubles the levels (24.0 V and 23.2 V for lead-acid). Once the app sees a 24 V reading, it shows them doubled.

The glow plug's dip never counts

The glow plug draws a lot while the heater lights: a 12.9 V battery can read 10.7 V for a couple of minutes. So readings count only:

  • with the heater off (the battery at rest), on heaters that measure the voltage then. Many measure it only while they run: when they're off, they repeat the last reading from the end of the cooldown, and the app ignores it;
  • while it heats, from 2 minutes after the flame.

The self-check, ignition and cooldown never count (many heaters run the glow plug again while they cool down). And the voltage has to stay low for your full Must stay low for time, so no warning or stop comes from the start-up.

While the battery is low

Nothing starts the heater on its own: not King Thermostat, timers, Heat Schedules or Settings Guard's Keep running. The app's own Start asks first. It counts as recovered 0.3 V above the higher of your levels (on a charger, or with the engine running). On a heater that measures only while it runs, that's a reading from its next run.

Good to know

The heater measures the voltage at its own terminals. While it runs, long or thin cables read a little lower than the battery itself. The app shows the heater's reading only while it's live: on heaters that measure only while they run, the voltage in the big card's corner is empty while they're off. For exact battery state, a battery monitor is better; Battery Saver is the heater's own safety net.

Your heater has its own low-voltage cut-off too, usually lower. Battery Saver can stop earlier, so the battery isn't drained as far.

Same help as in the app (More → How to use).