Battery Life

Features

• Both mAh and Wh supported; mAh converts via `Wh = mAh × V / 1000`
• ⚠️ Realistic runtime includes efficiency, ageing and temperature, listed apart from the theoretical figure
• ⚠️ Ageing is counted as `× (1 − loss)` — a capacity loss
• ⚠️ The temperature factor comes from an empirical range (roughly 55%–85% of capacity in the cold)
• Runtime compared across light / medium / heavy loads
• Load can be given as current (mA) or power (W)
• The result states the method and that mAh is not comparable across voltages
• Computed locally with no network requests

How to use

1. Enter the capacity and pick mAh or Wh (enter the voltage for mAh)
2. Enter the load as current (mA) or power (W)
3. Enter the conversion efficiency and ageing loss, or leave the defaults
4. Pick the temperature band (low / normal / high)
5. The right-hand side gives theoretical and realistic runtime plus the three load cases

FAQ

Why do a 5000 mAh phone and a 5000 mAh power bank not last the same?

Because mAh is charge, not energy. Energy is `Wh = mAh × V / 1000`: a phone battery at about 3.7 V gives 18.5 Wh for 5000 mAh, while many power banks rate the cells at 3.7 V but output 5 V, so usable energy is further reduced by conversion losses. To compare, convert everything to Wh and then look at the load in watts. This tool does that conversion and reports the result in Wh.

What ageing loss should I enter?

Zero for a new battery; 10%–20% after a year or two if the drop is noticeable; 30%+ for a well-used one. It means the capacity lost since new, a decrease (the tool applies `× (1 − loss)`). It is separate from temperature: ageing is a permanent loss, temperature is a change in the capacity available right now.

Why does cold cost so much?

Cold raises the electrolyte’s viscosity, slows lithium-ion diffusion and increases internal resistance, so usable capacity falls noticeably. Around 0 °C only 55%–85% of the room-temperature capacity typically remains, and colder is worse; returning to room temperature usually restores it. It is an empirical range, varying greatly with cell chemistry, discharge rate and insulation, which is why the tool uses a mid-point rather than a precise value.