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"How long will it last" means two different things: how many hours it runs your loads on one charge, and how many years the battery survives. Here is how to think about both, with simple math you can copy.
Start with the battery's usable energy. A 48V 100Ah LiFePO4 module holds about 5.1 kWh (48V × 100Ah ≈ 5,120 Wh). LiFePO4 lets you use most of that, so plan on roughly 90% usable, or about 4.6 kWh per module.
Then divide by your load:
Runtime (hours) ≈ usable kWh ÷ load in kW
Real-world runtime is a little lower once you account for inverter efficiency and very high surge loads, so keep a margin. To size a whole system rather than a single battery, pair this with our buyer's guide.
Check a power bill for your daily kWh, or add up the big loads. Most homes that want meaningful backup land somewhere between 10 and 30 kWh of storage. That is two to six 48V 100Ah modules — exactly the kind of bank a rack is built to grow into.
LiFePO4 rack batteries are typically rated for several thousand cycles. At roughly one cycle a day, a battery rated for 6,000 cycles can last many years before it drops to its end-of-warranty capacity — far longer than lead-acid, which is why the higher up-front price pays back over time.
Two habits extend that life: avoid sitting at 100% or 0% for long periods (the "20/80" idea of favoring the middle of the range helps), and keep the battery in a reasonable temperature range. Many rack models add self-heating so they can charge safely in the cold.
Pricing moves with the market, so check current listings rather than a fixed number — but the useful metric is cost per usable kWh, not the sticker price. A larger module or a multi-module bank almost always costs less per kWh than a single small battery, and LiFePO4's long cycle life lowers the lifetime cost further.
See current pricing on our server rack batteries and solar batteries, and if you are building a full system, the solar panel kits collection bundles panels, inverter, and storage.
How long will a 48V 100Ah battery last?
About 5.1 kWh of stored energy — roughly 9 hours at a 500W load, or 4–5 hours at 1,000W, per module.
How long will a 20kWh battery last?
Around 18–20 hours at a 1,000W average load, or a few hours under heavy whole-home draw. Divide 20 kWh by your load in kW for a quick estimate.
What is the lifespan of a 48V LiFePO4 battery?
Commonly several thousand cycles — often many years at about one cycle per day — before it reaches its rated end-of-life capacity.
What is the 20/80 rule for batteries?
A rule of thumb to favor the middle of the charge range rather than constantly topping to 100% or draining to empty, which can help longevity. LiFePO4 is more tolerant than older chemistries, but the habit still helps.
This article is general information and uses rounded rules-of-thumb, not electrical or professional advice. Actual runtime and lifespan depend on your specific equipment, loads, and conditions. Follow the manufacturer's manual and local codes, and consult a licensed installer when in doubt.