How Long Will a 400Ah Battery Last?
A 400Ah battery bank at 12V provides 4,800Wh of capacity - the upper practical limit for 12V systems. At this capacity, most builders transition to 24V or 48V for better efficiency and lower cable costs.
Capacity
400Ah
Total Energy (12V)
4800Wh
Usable (80% DoD)
3840Wh
Typical Use
Off-grid homes
Runtime Calculator
Runtime at 100W
32.6 hours
1.4 days if running continuously
Total Capacity
4800Wh
Usable (80% DoD)
3840Wh
Solar Charging
* Actual runtime varies based on temperature, battery age, and load consistency.
Runtime Examples at 400Ah
| Device | Power Draw | Runtime |
|---|---|---|
| Fridge | 50W | 64 hours |
| Multiple devices | 100W | 32 hours |
| Power tools | 500W | 6.4 hours |
| High-power tools | 1000W | 3.2 hours |
| Space heater | 1500W | 2.1 hours |
* Based on 12V LiFePO4 with 80% depth of discharge and 85% inverter efficiency.
- ✓Large off-grid systems
- ✓Workshop backup
- ✓Extended power outage prep
- ✓Transitioning to 24V/48V
- ✗New 12V installations (use 24V instead)
- ✗Portable applications
- ✗Simple setups
400Ah Battery Tips
- •Strongly consider 24V or 48V at this capacity
- •12V at 400Ah requires very thick cables (2/0 AWG or larger)
- •Can handle regular 1000W inverter loads
- •Four 100Ah batteries in parallel is common but 24V is better
- •Pair with 800W+ solar for sustainable daily use
Frequently Asked Questions
Why switch to 24V or 48V at 400Ah?
Higher voltage means lower current for the same power. 12V at 400Ah pushing 2000W = 167A requiring huge cables. 24V cuts that to 83A, 48V to 42A. Smaller cables, less voltage drop, better efficiency.
How much solar for 400Ah?
Minimum 600W, ideally 800-1000W for reliable daily recharging. At 400Ah you are likely using significant power daily, so robust solar is essential.
Can 400Ah run an air conditioner?
A small 5000 BTU window AC (500W) could run for about 6 hours. Not practical for regular AC use - you need much larger capacity or accept generator dependence for AC.