Four ways to approach home storage
The useful question is not simply “which battery is cheapest?” It is how much usable energy and power you get from a complete system, and how much equipment choice you want to handle yourself.
Complete branded battery
A packaged battery and inverter ecosystem, normally supplied and commissioned as one installation.
Rack-mount 48/51.2 V LFP
Ready-made modules with an internal BMS, paired with a documented low-voltage inverter.
DIY 16S prismatic LFP
You choose the cells, BMS, enclosure, fuses and disconnects. It takes more work but gives you control over capacity and parts.
Second-life EV battery
A used EV pack can be extremely cheap per kWh, but you need evidence of its remaining capacity and a supported way for the pack and inverter to communicate.
Prices move too quickly for a trustworthy permanent range. Use dated quotations in the battery cost comparison; do not let an invented market average choose the winner.
The parts form one chain
Stores energyBMS / controller
Reports limitsFuse + disconnect
Protects and isolatesInverter / charger
Converts powerHome / grid
Uses and exchanges AC
Temperature sensing, current measurement, containment and monitoring support the chain. A BMS watches the battery; it does not replace the main fuse or a correctly rated disconnect.
Size energy and power separately
A large battery does not automatically run a large load. Battery current limits and inverter power set the ceiling. Use the main calculator to estimate the capacity and power your household can use.
Cheap battery or cheap complete system?
Start with the battery price, then add only what that route still needs: BMS or controller, inverter, protection, enclosure, cables, monitoring and installation. A complete EV pack may already contain contactors, current sensing, temperature sensors and a strong enclosure, so do not price those twice. Equally, loose LFP cells are not yet a working home battery.
Let the numbers decide. A second-life EV system can remain remarkably inexpensive after integration, while a rack system may win where labour, warranty and expandability matter more.
Keep the boundary clear: Planning the architecture and choosing low-voltage parts are different from connecting storage to household mains. Removed EV packs can retain lethal voltage; opening packs, defeating interlocks and live high-voltage work are outside this guide.
Turn the idea into numbers.
Compare battery-only and complete-system cost using your own evidence.
Choose your next guide
Useful technical sources
- Energy Saving Trust battery-storage guidance.
- Energy Networks Association storage connection guidance.
- Battery-Emulator project documentation for supported EV-pack and inverter integrations.