Inputs
Energy result
Understanding Ah vs kWh
What's the difference?
Amp Hours (Ah) measures a battery's charge capacity — how much current it can deliver over time. Kilowatt Hours (kWh) measures total energy storage, which is more useful for comparing batteries at different voltages.
Why voltage matters
A 100Ah 12V battery and a 50Ah 24V battery both store the same energy (1.2 kWh), but they're suited for different applications:
- 12V systems — RVs, boats, small off-grid setups
- 24V systems — Larger RVs, medium solar systems
- 48V systems — Home battery backup, large solar installations
Depth of discharge (DoD)
Not all battery capacity is usable. DoD tells you how much you can safely use:
Lead-acid
50% DoD recommended — using more reduces lifespan significantly
LiFePO4
80–90% DoD safely usable — longer lifespan at any depth
Real-world solar examples
Lead-acid vs lithium
Lead-acid bank
4 × 6V 225Ah in series for 24V
- Total: 5.4 kWh
- Usable (50% DoD): 2.7 kWh
LiFePO4
1 × 48V 100Ah
- Total: 4.8 kWh
- Usable (90% DoD): 4.32 kWh
Despite lower raw capacity, the lithium battery delivers 60% more usable energy.
DIY LiFePO4 vs Tesla Powerwall
Tesla Powerwall 2
13.5 kWh at ~50V = ~270Ah
DIY build
4 × 3.2V 280Ah EVE cells in series
51.2V × 280Ah = 14.34 kWh (12.9 kWh usable) at roughly half the cost
Sizing overnight backup
Average US home uses ~30 kWh/day. Overnight (6pm–6am) is roughly 12 kWh. At 48V: 250Ah needed. With lithium (90% DoD): 278Ah. With lead-acid (50% DoD): 500Ah — showing why lithium needs roughly half the Ah capacity.
When you'll need this conversion
A 12V 200Ah battery and a 24V 100Ah battery both store 2.4 kWh. Without converting, the 200Ah battery appears to have "twice the capacity" — a common misconception.
A 48V 200Ah LiFePO4 battery ($2,400) stores 9.6 kWh (8.64 kWh usable at 90% DoD). Cost per usable kWh: $278. Over 4,000 cycles: $0.069/kWh/cycle.
A solar array producing 6 kWh on a typical day needs 125Ah at 48V for nighttime storage. With 90% DoD, the bank needs at least 139Ah at 48V.
