How do I calculate robot battery runtime?

Runtime in hours = usable capacity in Ah divided by average current draw in amps. Usable capacity is less than rated capacity: around 80% for LiPo, 85% for Li-ion and NiMH, and only about 50% for sealed lead-acid.

What C-rating does my battery need?

Minimum C-rating = peak current draw divided by capacity in Ah. A robot pulling 30 A peak from a 2 Ah pack needs at least 15C; choose a pack rated with comfortable margin above that.

Why does my robot run for less time than calculated?

Real current draw is usually higher than estimated: motors draw surge current on every start, voltage sag increases current for the same power, and capacity fades with age and cold. Budget with the usable-capacity derating this calculator applies.

Robot Battery Runtime Calculator — mAh to Minutes

How this calculator works

The core relationship is simple:

Runtime (hours) = Usable capacity (Ah) ÷ Average current (A)

The part most calculators get wrong is usable capacity. You should never drain a battery to zero: LiPo cells are damaged below ~3.0 V/cell and most builders land at about 80% usable; lead-acid packs lose lifespan dramatically past 50% discharge. This tool applies those deratings automatically per chemistry.

The C-rating check divides your peak current by capacity in Ah. If your robot can demand 12 A from a 2.2 Ah pack, you need at least a 12 ÷ 2.2 ≈ 5.5C pack — and because manufacturers' C-ratings are optimistic, choose a pack rated at roughly double the minimum.

Estimating average current: a small 2-motor indoor robot typically averages 1–4 A; a 4-motor outdoor rover 5–15 A. Motor datasheets list current at rated load — sum your motors, add ~0.5 A for logic, camera and sensors.

Common questions

Does higher voltage give longer runtime?

Not by itself. Energy is voltage × capacity (Wh). A 7.4 V 2200 mAh pack stores 16.3 Wh; an 11.1 V 2200 mAh pack stores 24.4 Wh — more energy, but your motors will also draw more power at higher voltage. Compare packs in watt-hours, not mAh.

Can I use the mAh printed on cheap packs?

Treat unbranded capacity claims with suspicion — cheap cells often deliver 50–70% of the label. If runtime matters, test the pack with a battery analyzer or buy cells with published test data.

Parts this calculation leads to

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LiPo Packs

2S–4S packs with real C-ratings for drive systems.

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Li-ion Cells & Holders

18650/21700 cells for long-runtime rovers.

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Chargers

Balance chargers — never charge LiPo without one.

Browse balance chargers →

Battery Monitors

Low-voltage alarms and power meters.

Browse voltage alarms →