What it is
A server-rack battery is a 48-volt LiFePO4 (lithium iron phosphate) battery built in the same flat, slide-in shape as computer servers. Each one stores about 5 kWh, and you stack them in a rack to get as much storage as you need.
They've become the standard for house-size solar because they hit the sweet spot: a good price per kWh stored, simple to expand, and they talk directly to the inverter so the whole system stays in sync.
Why 48 volts
Higher voltage means less current for the same power, so wires can be thinner and less energy is lost as heat. For anything house-sized, 48 volts is the norm. 12 volts is for vans and small rigs.
How many you need
| Daily use | Days without sun | Stored | Batteries (≈4.6 kWh usable each) |
|---|---|---|---|
| 4 kWh (cabin) | 1.5 | 6 kWh | 2 |
| 7 kWh (tiny house) | 1.5 | 10.5 kWh | 3 |
| 15 kWh (off-grid home) | 1.5 | 22.5 kWh | 5 |
| 25 kWh (big home) | 1.5 | 37.5 kWh | 9 |
Want your exact number? Use the battery bank calculator, or start a guide and it sizes the whole system for your darkest month.
Which one
The EG4 LifePower4 is what a large share of DIY home systems run: about 5 kWh each, many units on one rack, and it works out of the box with EG4's inverters. Independent tester Will Prowse covers server-rack batteries in depth, and you can see full homes running them in See it running.
Good to know
- Heavy: plan on two people per battery.
- No charging below freezing: keep them indoors.
- Usable vs. rated: you can use about 90% of a LiFePO4 battery every day, far more than lead-acid.
- Lifespan: rated for thousands of cycles, well over a decade of daily use.
Questions people ask
How many server-rack batteries do I need?
Take what you use in a day (kWh), multiply by the days you want to go without sun, and divide by about 4.6 kWh usable per battery. A tiny house using 7 kWh a day with a day and a half of cushion needs about 3.
Can I add more server-rack batteries later?
Yes. That's one of their biggest advantages. They stack in parallel on the same rack, so you can start with a few and add more as life grows.
Can server-rack batteries go in a van?
Usually not. They're heavy and run at 48 volts, while vans are built around 12 volts. Vans do better with 12V lithium batteries.
Do server-rack batteries work in the cold?
They can sit in the cold, but like all lithium batteries they can't charge below freezing. Keep them indoors or in an insulated space.
Get the exact setup
A few taps and you'll know exactly what to buy for your situation.