Battery Life (mAh)

Battery life from mAh: how long it really lasts

Start with runtime_h = capacity_mAh / load_mA. To get closer to reality, knock that figure down by an efficiency factor of around 85%, because voltage regulation, heat and standby circuits all eat into the budget. Take a 4,500 mAh phone pulling 200 mA on average. That works out to 22.5 h on paper but more like 19 h once you account for the losses. A racing drone with 2,200 mAh feeding a 20 A motor barely manages 6.6 minutes. The same idea scales up to energy: a Tesla Model 3 carrying 75 kWh and using 200 Wh/km goes about 375 km, while long-range EVs pack 60-80 kWh for 300-500 km. You'll run into a handful of chemistries. Li-ion shows up in phones and laptops. LiFePO4 powers BYD EVs and solar storage, where its safety and longer cycle life matter. NMC goes into Teslas for its high energy density, and solid-state is the one everyone's waiting on. Temperature plays into all of this too, since cold can shave 20-30% off the usable capacity.

Applications

Planning a camping or off-grid setup, estimating drone flight time, dealing with EV range anxiety, working out how long an IoT sensor will last, picking a power bank for a trip, or sizing a UPS.

FAQ

Why does my phone die faster than the formula says? Because an average draw hides the spikes. Fire up 5G, GPS, the screen and the camera together and you can be pulling 5-10× what the phone sips at idle.

How do I compare mAh between phones of different brands? Convert both to Wh with Wh = mAh × V / 1000. Since most cells sit at 3.7-3.85 V, the comparison ends up being close to direct anyway.

Does cold reduce battery life? It does. Drop below 0 °C and lithium temporarily gives up 20-30% of its available capacity. Warm the battery back up and most of that comes back.