Updated October 2026
Winter
Heated blanket runtime calculator
Will your battery last the night? Plug in your blanket and battery numbers — get your safe runtime in seconds.
Estimated runtime
Above typical 12V socket limits. Most 12V accessory sockets are fused at 10–15 A (roughly 120–180 W). A blanket drawing this much needs direct battery wiring — not a cigarette-lighter socket.
Won’t last a full night’s rest. On this battery, the blanket dies before morning. You’d need to run the engine periodically, add battery capacity, or both.
- Don’t run it overnight on a starter battery. Draining the cranking battery can leave you unable to start in the morning — and cold weather both shrinks battery capacity and makes the engine harder to turn over. If you must, run the engine periodically through the night.
- Respect the socket’s fuse. Check the blanket’s wattage against your 12V socket’s rating before plugging in. When in doubt, wire direct to the battery with an inline fuse.
- Real blankets cycle on and off. Most 12V heated blankets use a thermostat, so real-world runtime is often longer than this worst-case continuous-draw math.
- A blanket is not cab heating. It keeps one person warm under covers — it does not heat the cab, prevent fuel gelling, or replace idling. The honest idle-reduction bundle is a compressor cooler plus a fuel-fired cab heater.
Fits this use case
Stalwart 12V heated car blanket — plugs into the same 12V socket this calculator is about, draws well under typical socket fuse limits, and its thermostat cycles on and off so real-world runtime beats this worst-case math.
Affiliate disclosure: the link below is an Amazon affiliate link. As an Amazon Associate, The Driver Gear earns from qualifying purchases. Research-based. We did not test these hands-on. Scores come from published specs and driver reviews.
Math: runtime (hours) = battery Ah × volts × discharge limit ÷ blanket watts. Worst-case estimate assuming continuous draw.
Research-based. We did not test these hands-on. Scores come from published specs and driver reviews.
Research-based. We did not test these hands-on. Scores come from published specs and driver reviews. Every default on this page is a published figure or a labelled assumption — change any input and the math re-runs.