What can a 300Ah 12V battery power?
A 300Ah 12V LiFePO4 battery holds about 3.6 kWh, of which roughly 2736 Wh is usable. Here is roughly how long it runs common devices — adjust any load in the calculator below.
| Device | Typical power | Run-time |
|---|---|---|
| Refrigerator | 150 W | 18.2 hours |
| CPAP | 45 W | 60.8 hours |
| TV | 90 W | 30.4 hours |
| Laptop | 50 W | 54.7 hours |
| LED lights | 40 W | 68.4 hours |
| Space heater | 1500 W | 1.8 hours |
| Ceiling fan | 60 W | 45.6 hours |
| Router | 12 W | 228.0 hours |
Calculate for your device
Run-times assume LiFePO4 (~80% usable) and typical inverter loss. Lead-acid of the same rating gives roughly 60% as long, since only ~50% is usable. To build a full system, use the system calculator.
Typical use
At 2,736 Wh usable, a fridge runs about 18 hours — a full day and then some — which is why 300Ah at 12V is a common DIY size for off-grid cabins built around a single high-capacity 12V bank rather than a series-wired higher-voltage system.
Compare nearby sizes: 3kWh battery · 100Ah 48V battery
Frequently asked questions
How many watt-hours is a 300Ah 12V battery?
A 300Ah 12V battery is about 3.6 kWh (3600 Wh nominal). On LiFePO4 roughly 2736 Wh is usable; on lead-acid about half is.
What can a 300Ah 12V battery run?
A 300Ah 12V LiFePO4 battery (~2736 Wh usable) can run, for example, a 150W refrigerator for about 18.2 hours, or LED lights (40W) for about 68.4 hours.
Sources & standards
- IEEE 1013 — Recommended Practice for Sizing Lead-Acid Batteries for Stand-Alone Photovoltaic Systems — Widely used engineering practice for days-of-autonomy and depth-of-discharge sizing methods, referenced here for the general sizing approach.
- UL 1973 — Batteries for Use in Stationary and Motive Auxiliary Power Applications — Safety standard most LiFePO4 and other stationary/portable battery packs are certified to.
- IEC 60896 — Stationary Lead-Acid Batteries (test & performance requirements) — International test standard covering VRLA (AGM/gel) and flooded stationary lead-acid batteries.
Estimates for planning only. See the methodology.