Battery Bank Calculator
Series/parallel battery pack voltage, Ah, Wh and runtime.
About this tool
Pick a cell or battery type (or enter your own voltage and capacity), then the number in series and in parallel. Add the load, usable depth of discharge and inverter efficiency to estimate runtime.
Series, parallel and runtime
Batteries in series add voltage at the same capacity; batteries in parallel add capacity at the same voltage. Packs are written SรP: four 3.2 V, 100 Ah LiFePO4 cells in series (4S1P) make a 12.8 V, 100 Ah, 1,280 Wh bank, and a 13S4P pack of 3.6 V, 3 Ah Li-ion cells is a 46.8 V, 12 Ah, 562 Wh e-bike battery. Energy in watt-hours (V ร Ah) sets runtime: hours = Wh ร usable depth of discharge ร efficiency รท load watts. The 12.8 V bank powering a 200 W load through a 90%-efficient inverter, using 90% of its capacity, runs about 5.2 hours. Lead-acid batteries last longest when discharged to only about 50%; LiFePO4 handles 80โ90% routinely. The C-rating gives the maximum continuous current: 1C on a 100 Ah bank is 100 A. Honest limits: connect only matched cells at the same state of charge, use a battery management system for lithium, and fuse each parallel string. Capacity drops in cold weather and at high current. Not electrical advice. The battery life calculator and the solar panel calculator are related.
Frequently asked questions
How do I calculate battery bank capacity?
Voltage = cell voltage ร cells in series; amp-hours = cell Ah ร strings in parallel; watt-hours = volts ร amp-hours.
How long will a 100Ah 12V battery last?
With LiFePO4 (12.8 V, 90% usable) through a 90% inverter, about 5.2 hours at 200 W. Lead-acid at 50% usable gives roughly 2.7 hours.
What does 4S2P mean?
Four cells in series per string, with two strings in parallel.
Should I wire batteries in series or parallel?
Series for a higher system voltage, which means lower current and thinner cables; parallel for more capacity at the same voltage.
Is my data sent anywhere?
No. Everything is calculated in your browser, and nothing is stored or sent.