One battery says 14 Ah, another 500 Wh, a power bank promises 20,000 mAh. Which holds more energy? Once you know how watt-hours (Wh), amp-hours (Ah) and volts (V) relate, comparing batteries and planning solar charging gets easy.
The one formula
Energy (Wh) = voltage (V) × capacity (Ah)
- 36 V × 14 Ah = 504 Wh
- 48 V × 10.4 Ah = 499 Wh – practically the same energy.
Amp-hours alone say nothing without the voltage. That’s why Wh is the number to compare – for batteries, solar yield and consumption alike.
Three things the label doesn’t tell you
- Usable capacity is lower than the label: the BMS keeps a reserve, cold weather and age take their share.
- The voltage moves: the label shows the nominal voltage; full and empty are quite different.
- Power banks are rated in mAh at about 3.7 V – 20,000 mAh is only around 74 Wh, a fraction of an e-bike battery.
From Wh to kilometres
Divide usable energy by consumption: at about 10 Wh/km, 450 Wh give roughly 45 km of assisted riding. How much a sunny day adds is covered in how many watts of solar you need, and how consumption changes with terrain and load in calculating solar e-bike range.
More on the cells themselves: lithium-ion batteries and LiFePO4 vs. NMC. And why every kWh keeps getting cheaper: battery prices hit a record low.
