How home batteries actually work

The chemistry in one move

A lithium battery stores energy by physically relocating lithium ions. Charging uses electrical energy to push ions from the cathode across a separator into the anode, where they're held like a compressed spring. Discharging lets them flow back, and the accompanying electron flow through your circuits is the power that runs your home. No combustion, no moving parts - just ions shuttling back and forth, thousands of times.

Most home batteries - including the ranges we install - use lithium iron phosphate (LFP) chemistry, chosen over the cobalt chemistries in phones and many EVs because it trades some energy density (irrelevant on a garage wall) for markedly better thermal stability and cycle life. It's the sensible chemistry for a box that lives beside your house for fifteen years.

Nominal, usable, and why the gap exists

Battery capacity comes in two numbers. Nominal is the chemistry's theoretical total; usable is what you can actually cycle. The gap is deliberate: draining lithium cells to true zero or brimming them to true full accelerates their ageing dramatically, so the battery management system fences off buffer zones at both ends.

A larger usable-to-nominal ratio generally reflects confident engineering, and usable is the only number that belongs in your arithmetic - it's the figure we quote and the one to compare across brands. Marketing that leads with nominal capacity is telling you about the spring, not the stroke.

Degradation, honestly

Every cycle shuffles ions through microscopic structures that very gradually wear - so capacity declines with use, typically to a warranted floor of around 60-80% of original after ten years, depending on the product. This is normal physics, not defect, and it's precisely what battery warranties regulate: a promised capacity retention over a term, usually with throughput or cycle conditions attached.

Practical consequences: heat is the great accelerant (why installation standards care about location, and shaded southern walls beat western sun), and a battery sized with slight headroom today still meets your load in year twelve.

The BMS: the adult in the room

Wrapped around the cells sits the battery management system - electronics that balance individual cells, police temperature, enforce those charge fences, and coordinate with your hybrid inverter about when to charge, discharge, or hold reserve for backup. When a VPP dispatches your battery, it's negotiating with the BMS; when a blackout hits, the BMS and inverter execute the islanding.

It's the reason a home battery is an appliance rather than a science project - and why the software maturity of a manufacturer matters nearly as much as its chemistry. How that stored energy earns its keep is the economics article; this is the machinery underneath it.