Formulas used
- Backup hours = battery V x Ah x usable depth x inverter efficiency / load W
- Battery Ah = load W x hours / (efficiency x battery V x depth)
Frequently asked questions
Why is real backup shorter?
Battery age, temperature and high discharge currents all reduce usable capacity. Expect 10 to 20 percent less than the calculated value.
What depth of discharge should I use?
Tubular lead-acid batteries last longest at about 50 percent. LiFePO4 batteries can use 80 percent or more.