How many batteries do I need for my inverter?
Batteries and inverters have to match twice over: the bank must deliver the current the inverter draws at full output (and its surges), and it must store enough energy to run your loads between charges. Miss the first and the BMS cuts out mid-surge; miss the second and you are dark by morning.
The first constraint is what compatibility checking is about, and it is where undersized banks fail loudly: a single small battery often cannot legally feed a large inverter no matter how little energy you use.
How it works
Current: the inverter's continuous watts divided by battery voltage is the draw the bank's combined BMS continuous rating must cover with headroom, and motor-start surges push well past continuous. Batteries in parallel add their BMS current ratings, which is often the real reason a build needs a second battery.
Energy: daily watt-hours times the days of autonomy you want, adjusted for usable depth of discharge, gives bank capacity. LiFePO4 makes most of its rated capacity usable and tolerates deep cycling far better than lead chemistries, which is why it dominates modern off-grid builds.
Common questions
What is the difference between capacity and current capability?
Capacity (amp-hours) is how much energy the bank stores; BMS current ratings are how fast it may be drained. An inverter can be starved by a bank that has plenty of energy but too little continuous current rating.
Why does the BMS continuous rating matter so much?
Because it is a hard cutoff, not a suggestion. Exceed it and the BMS disconnects to protect the cells - usually at the worst moment, like a pump or compressor start.
Can I mix battery brands or ages in one bank?
Do not. Different internal resistance and BMS behavior make batteries share current unevenly, aging the weakest fastest. Matched batteries from the same model line are the rule.
How do surges factor in?
Motors briefly draw several times their running power, and the inverter passes that to the battery. Banks need surge headroom via BMS peak ratings or extra parallel batteries; the checks flag pairings where surge exceeds what the bank publishes.
Pair any battery and inverter in the builder and the checks verify continuous draw and surge headroom against the BMS ratings, math shown.
Open the builderThese guides are educational and qualitative on purpose - the numeric answers depend on your exact components, and the builder computes them with every formula shown. Always verify a final design with a licensed professional.