Solar Battery Comparison Chart
Battery capacity is quoted nominally and delivered usably, and the gap between the two differs enormously by chemistry. A 10 kWh lead-acid bank yields around 4 kWh in practice; a 10 kWh lithium bank yields over 8.
Generated from the same data the calculators use — a chart and a calculator on this site cannot disagree.
Usable capacity by chemistry
| Chemistry | Depth of discharge | Round-trip efficiency | Usable fraction | Usable from 10 kWh nominal |
|---|---|---|---|---|
| Flooded lead-acid | 50% | 80% | 40% | 4.0 kWh |
| AGM / sealed lead-acid | 50% | 85% | 43% | 4.3 kWh |
| LiFePO4 | 90% | 95% | 86% | 8.6 kWh |
Practical differences
| Chemistry | Typical cycle life | Cold weather | Maintenance |
|---|---|---|---|
| Flooded lead-acid | ~1,200 cycles at 50% DoD | Loses ~20% capacity near freezing | Watering and ventilation required |
| AGM / sealed lead-acid | ~800–1,200 cycles at 50% DoD | Loses ~20% capacity near freezing | Maintenance free |
| LiFePO4 | 3,000–6,000 cycles at 80% DoD | Must not charge below freezing without a heater | Maintenance free, BMS required |
How to read this chart
Compare cost per usable kilowatt-hour over the bank’s life, not cost per nominal kilowatt-hour. Lithium typically costs two to three times more up front and delivers twice the usable energy across three to five times the cycles.
Depth of discharge on lead-acid is an economic limit rather than a physical one. You can take more, but cycle life falls sharply — a flooded battery taken to 80% may manage a third of the cycles it would at 50%.
Round-trip efficiency is energy recovered divided by energy stored. The remainder becomes heat during charge and discharge, and on lead-acid also gassing near full charge.
Charging LiFePO4 below 0 °C causes lithium plating and permanent capacity loss. Batteries in unheated spaces need internal heaters or a battery management system that blocks charging until they warm. Discharging in the cold is fine.
Sources
- Typical depth-of-discharge limits and round-trip efficiencies by chemistry
- Published cycle life ranges at stated depth of discharge
Reference values. Manufacturer specifications govern depth of discharge, cycle life and temperature limits for any specific product.
Frequently asked questions
Why can I only use half a lead-acid battery?
You can physically take more, but cycle life collapses. The 50% figure is where the economics stop making sense, not where the battery stops working.
Is lithium worth the price?
On a bank that cycles daily, usually yes on cost per usable kilowatt-hour over its life. On a backup bank that cycles a few times a year, calendar life rather than cycle life governs and the cheaper chemistry can win.
What is round-trip efficiency?
The fraction of energy you get back compared with what you put in. Around 95% for lithium and 80 to 85% for lead-acid, with the difference lost as heat.
Does system voltage change capacity?
No. It changes the current needed to move the same energy, which determines conductor and fuse sizes. Higher voltage means smaller and cheaper wiring for the same kilowatt-hours.