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Battery runtime calculator

How long a battery runs a load.

Try the circuit in the labBuild it on the simulator's bench and measure it.

How it is worked out

Runtime = capacity × voltage × usable fraction ÷ load power. Energy in watt-hours is Ah × V; the load draws more than its own rating because the converter in between wastes some.

Example: a 12.8 V 6 Ah LiFePO4 pack holds 77 Wh. Using 90 % of it through a 90 %-efficient converter to run 10 W: 77 × 0.9 ÷ (10 ÷ 0.9) = 6.2 h.

Usable depth: LiFePO4 80–95 %, Li-ion 80–90 %, lead-acid 50 % (deeper discharge shortens its life sharply). Cold and high currents reduce the capacity you get.

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