LifeTally
Power bank charge calculator
How many full charges could my power bank provide?
Compare battery energy using your own capacities, nominal voltages and overall efficiency.
Your batteries and efficiency
Pair each mAh value with its own stated nominal battery voltage, not the USB output voltage. If the label lists Wh, check that the pair reproduces it. Do not mix summed cell capacities with a series-pack voltage.
How the estimate works
Convert each capacity to energy: Wh = mAh × nominal V ÷ 1000. Apply your overall efficiency to the bank energy, then divide by device energy. Overall efficiency covers the entire path, including bank, cable and device losses.
E = mAh × V ÷ 1000
U = Ebank × η ÷ 100
Q = U ÷ Edevice
N = floor(Q)Assumes a fully charged power bank and identical device charges from 0 to 100%. Efficiency is your assumption, not a recommended value. Device use during charging, aging, temperature and changing losses are not modeled. This does not predict charging speed, compatibility or guaranteed real charges.
Anker: battery capacity, voltage and energy ↗Anker: losses in the bank and receiving device ↗
Check the filled example
Chosen example: 20000 mAh at 3.7 V; device 5000 mAh at 3.85 V; overall efficiency 77%. Energies: 74 Wh and 19.25 Wh; usable energy 56.98 Wh. This gives 2.96 charge equivalents, or 2 full charges in the model. These inputs are illustrative, not battery or efficiency norms.
Accepted input values
- Power bank battery capacity, mAh
- 20000
- Power bank nominal battery voltage, V
- 3.7
- Device battery capacity, mAh
- 5000
- Device nominal battery voltage, V
- 3.85
- Overall energy efficiency, %
- 77