Inputs
Energy result
Understanding battery capacity
Amp hours vs watt hours
Amp Hours (Ah) measures how much current a battery can deliver over time at a specific voltage. Watt Hours (Wh) measures total energy stored, making it the true measure for comparing batteries regardless of voltage.
Why voltage matters
A 12V 100Ah battery and a 24V 50Ah battery appear very different, but both store exactly 1,200Wh of energy. The voltage determines the current level:
- 12V systems — RVs, boats, small off-grid setups (higher current, thicker wires)
- 24V systems — Larger RVs, medium solar systems
- 48V systems — Home battery backup, large solar installations (lower current, thinner wires)
When to use each unit
Use Wh
Energy- Compare batteries at different voltages
- Calculate how long loads can run
- Match battery to daily energy usage
Use Ah
Capacity- Size battery cables and fuses
- Select charge controllers
- Match wiring to current requirements
Real-world solar examples
12V 100Ah LFP battery
A 12V 100Ah lithium iron phosphate battery stores 1,200Wh (1.2 kWh). With 90% usable depth of discharge, you get about 1,080Wh — enough to run a 60W refrigerator for 18 hours.
Same energy, different voltage
24V 200Ah
24V × 200Ah = 4,800Wh
48V 100Ah
48V × 100Ah = 4,800Wh
Both store identical energy. The 48V system draws half the current, allowing thinner, cheaper wiring.
48V 100Ah battery bank
A 48V 100Ah lithium battery bank stores 4,800Wh (4.8 kWh) — approximately one-third of a Tesla Powerwall's 13.5 kWh capacity. Enough to run essential loads (fridge, lights, router) for a full day.
When you'll need this conversion
Two 12V 100Ah batteries provide 2,400Wh total. With 90% usable DoD on LFP, that is 2,160Wh usable — just enough for 2,000Wh of overnight loads, but with little margin.
A "12V 100Ah" and a "24V 50Ah" battery sound different but store identical energy: 1,200Wh. Without converting to Wh, buyers frequently overpay for batteries that appear larger based on Ah alone.
A 48V 100Ah battery bank (4,800Wh) needs recharging from 20% to 100% (3,840Wh). With 400W panels in 5 peak sun hours, each panel produces 2,000Wh/day. Two panels cover the recharge.
