Storage is the most expensive part of a backup system. Here are the specs that really matter so your battery lasts for years and keeps the house running exactly as long as you need.
Why LFP
Lithium iron phosphate batteries (LiFePO4, LFP) have become the standard for homes and businesses. They are safer than other lithium chemistries, do not tend to overheat and withstand thousands of charge cycles. Lead-acid batteries are cheaper upfront but last several times less.
Capacity: how many kWh you need
Work out what must run during an outage and for how many hours. A boiler with a pump, a fridge, a router and lighting in an average house use about 0.5–1 kW. To last 8 hours you need roughly 5–10 kWh of usable capacity.
Depth of discharge and cycles
Depth of discharge (DoD) shows how much of the capacity you can use without harming the battery. For good LFP batteries it is 90–95%. Cycle count is the lifespan: 6,000 cycles means more than 15 years of daily use.
Low voltage and high voltage
Low-voltage batteries (48 V) are simpler and cheaper and suit smaller systems. High-voltage modular systems are more efficient at high power and are easy to expand block by block. The key rule: the battery must be compatible with your inverter.
Where to install it
- In a dry room that stays above freezing: a boiler room, garage or utility room.
- Out of the sun and away from heat sources.
- With access for service and ventilation.
You can start with one or two modules and add more later: modern systems allow it.