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Most people buy too little battery or too much. The right size comes from one number: how many kilowatt-hours your home uses in the hours you want to cover. Get that number and the battery almost picks itself. This guide walks through the sizing math, how long a 10 kWh battery really lasts, and the 48V LiFePO4 batteries we carry at Krato Power to hit your target.
Size the battery to your loads and your hours, not to the size of your house. The rule of thumb:
Battery size (kWh) = the loads you run (kW) times the hours of backup you want.
An average US home uses about 30 kWh a day, but you rarely need to back up all of it. Decide what you are covering first:
A 48V 100Ah server rack battery is about 5.12 kWh, and these batteries stack, so you reach your target by adding modules.
Runtime is capacity divided by load. A 10 kWh bank gives you, very roughly:
These are estimates. Real runtime depends on how hard your appliances cycle and the efficiency of your inverter, but the pattern holds: the lighter the load, the longer the bank lasts.
The cheapest reliable system backs up essentials, not everything. Backing up a central air conditioner or an electric range multiplies both the battery and the inverter you need, because of the surge when big motors start. A common, cost-effective approach is to size the bank for essentials plus one or two comfort loads, and leave the heaviest appliances off backup. You can always add modules later.
Browse sizes in the 48V Server Rack Batteries collection, and match your inverter to your largest simultaneous load.
If you are charging from solar, size the array to refill the bank during the usable sun hours of a day. The rule of thumb: panel array (watts) roughly equals the kWh you need to replace divided by your daily sun hours, with headroom for losses.
To put back 10 kWh in a typical 4 to 5 sun-hour day, you want roughly 2,000 to 3,000 watts of panel. More sun or a smaller daily draw lowers that; a cloudy climate raises it. If you are not using solar, the grid or a generator refills the bank instead through an inverter charger.
All are 51.2V 100Ah (about 5.12 kWh) LiFePO4 modules, current pricing at Krato Power:
For cold climates, the self-heating SGH48100T at $1,150 keeps charging below freezing.
For a short time, or for essentials all day. It will not run a full house with HVAC and heavy appliances for long. For whole-home coverage through an outage, plan on 20 kWh and up, plus an inverter sized to your surge loads.
Take your daily kWh for the loads you are covering and match it. Essentials for 24 hours is often 5 to 10 kWh (one to two modules). Covering more circuits for a full day pushes you to 15 to 20 kWh (three to four modules).
Double the 10 kWh figures above: roughly 32 to 40 hours on essentials, far less on heavy loads. Runtime always comes down to your load.
More batteries extend how long you can run without sun; more panels refill the bank faster. For outage backup, prioritize battery capacity. For lowering your daily power cost, prioritize panels. Most systems want a balance of both.
Tell the Krato Power team your daily energy use and what you want to keep running, and we will size a battery and inverter to match. Call 888-855-7286 or start in the 48V Server Rack Batteries collection.
This is general information, not electrical or professional advice. Whole-home and grid-connected installs need a licensed electrician per local code.