Running a Diesel Heater All Night: What It Actually Costs Your Battery

The question arrives every October in the same shape. In this month’s r/VanLife battery threads (one, two), one owner wants a battery that can “handle a heater all night”, and another states the winter version of the problem exactly: “I don’t drive enough to use the alternator” plus “temps that restrict charging my battery inside cold temps.” Both askers are circling the same discovery, so this page just says it plainly: running a diesel heater overnight is one of the easiest jobs your electrical system will ever do — and getting the energy back into the bank on a freezing morning is one of the hardest.

The overnight math, stated honestly

A diesel air heater is a diesel appliance, not an electric one. The heat comes from burning fuel in a sealed exchanger; electricity only runs the combustion fan, the fuel-metering pump, and the controller. The published draw figures for 2kW-class units cluster in the same band:

Three things fall out of that curve. First, the overnight total is small: 10–25W across eight or ten hours is 80–250Wh, call it 8–15Ah from a 12V bank for a 2kW unit at typical output — a fraction of what a 12V fridge uses in a day, and nothing like the hundreds of watts the 12V air conditioners on the other side of this site’s climate coverage demand. If your bank can’t spare 15Ah, the problem predates the heater — size the bank with how many amp hours do I need first.

Second, the startup surge is the only demanding moment. The glow plug pulls on the order of 8–10A at 12V for two or three minutes while the burner lights. A hardwired battery bank doesn’t notice. The places it bites: power-station 12V ports with 10A limits (below), thin supply wiring, and half-dead lead-acid banks whose voltage sags under the surge — diesel heaters are famously grumpy about low voltage at ignition.

Third, and least obvious: a short-cycling heater multiplies the expensive moments. Every restart is another glow-plug cycle, so a heater that starts and stops all night — the classic symptom of an oversized unit forced to idle — burns meaningfully more electricity and fuel than one that settles at low output and hums. If that’s your heater, it’s probably too big, and the fix is sizing or control, not battery.

For reference, the budget-tier unit the cluster’s buyer’s guide currently points at — the VEVOR 2kW all-in-one (verified on Amazon this run) — publishes exactly this profile: 12V supply, app control, automatic altitude adjustment, and fuel figures in the 0.1–0.24 L/h band. And if your unit’s controller can’t hold a low idle at all, the universal LCD thermostat controller from the temperature-holding guide is the $25 control-layer fix.

The power-station trap: it’s the port, not the capacity

“Can I run a diesel heater off a power station?” is really two questions, and the marketing answers the easy one. Capacity: trivially yes — 150Wh a night disappears into even a small station. Output: check the regulated 12V port rating before you buy anything. Many stations cap their 12V accessory outputs at 10A (120W), and a glow-plug surge at 8–10A rides right at that ceiling — through a cigarette-plug adapter with its own voltage drop, ignition can brown out and fault. This is the same lesson as our power station 12V output ceiling piece, wearing a winter coat: the spec that matters is the port’s continuous and surge amperage, not the watt-hours on the lid.

The robust setups, in ascending order of permanence: a station whose 12V output is rated comfortably above 10A continuous, wired with the maker’s proper DC cable rather than a lighter-plug adapter; or skip the middleman and hardwire the heater to the house bank with an appropriately sized fuse, which is where every full-time winter build ends up anyway.

The real winter problem: the morning after

Here is the part the heater threads and the battery threads keep discovering separately. Most LiFePO4 packs will discharge happily well below freezing — and will refuse to accept a charge below about 32°F / 0°C. Charging cold lithium plates metal onto the anode and permanently damages cells, so any competent BMS simply blocks it. The battery that ran your heater faithfully through a 22°F night is, at 7 a.m., a battery that says no to your alternator.

That inverts where the money should go. The heater’s overnight draw never needed a bigger bank; the cold morning needs a smarter charging layer:

Engine-side, the DC-DC charger. When you do drive, you want the recovery to be fast and correctly managed. The Victron Orion XS 12/12-50A (verified on Amazon this run) is the current default — 50A, Bluetooth-configurable charge behavior — and the Renogy DCC50S remains the value alternative with a solar input built in, one box instead of two. Both are claimed specs, not our bench. Sizing the charger to your alternator and wiring it without cooking anything is its own subject, and it already has its own page: the DC-DC wiring guide published this week covers CCP2 connections, fusing, and grounds. Whether short winter drives can even pay the energy bill is the arithmetic in alternator charging cost per kWh.

Hookup-side, the shore charger. For campground or driveway nights, a proper multi-stage charger like the Victron Blue Smart IP65 12/7 (verified on Amazon this run) trickles the bank back overnight and holds it — 7A sounds small until you remember the heater only took 15Ah. Lithium-aware charge profiles matter here; a dumb float charger is the wrong tool.

And the thermal fix, which costs nothing: if your bank lives inside the insulated, heated envelope of the van, the same heater that drained it keeps it charge-ready. Banks mounted in unheated garages, boxes, or under-floor compartments are the ones that lock out. Some builders duct a trickle of heater output at the battery compartment; packs with built-in heaters and low-temp charge protection exist as a category. Per our standing policy we are not naming battery brands here — the chemistry constraint is universal, and the layout decision (bank inside the warm envelope) matters more than any badge.

The overnight checklist

• Fuel: expect roughly 1–2 liters per long night on a 2kW unit at published burn rates. Fill the tank in the evening; a heater that runs dry at 4 a.m. airlocks the fuel line and greets you with fault codes.
• Power: hardwired bank, or a 12V output rated above the glow-plug surge. No cigarette-plug adapters for permanent installs.
• Sizing and setting: low, steady output beats start-stop cycling for noise, fuel, and electrical draw alike. A heater that can’t idle low enough for your space is the sizing problem, again.
• Safety: exhaust terminated outside with sound joints, and a low-level CO detector mounted at breathing height. Non-negotiable, every night, and the reason that guide exists.
• Morning: if it froze overnight, don’t expect the bank to take charge until it warms. That’s chemistry, not a fault — plan the charging layer around it.

The one-sentence version: a diesel heater is the cheapest warm night your electrical system will ever buy, and the bill arrives in the morning — pay it with a charging layer built for winter, not a bigger battery.