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LiPo batteries: power for robots, and how to not set them on fire
Alessandro Panait·
Lithium Polymer (LiPo) batteries deliver high current and a lot of energy for their weight, which is exactly what a robot with motors needs. They are the standard choice, but they are not as forgiving as an AA battery.
Reading the label
- Voltage (S count): cells are about 3.7V each. A "2S" pack is ~7.4V, "3S" is ~11.1V. Match the pack to what your electronics and motors expect.
- Capacity (mAh): how much energy it stores. More mAh means longer runtime and more weight.
- C rating: how fast it can safely deliver current. Motors that pull big bursts need a decent C rating.
Powering a robot
Robots often use different voltages for different parts: a higher-voltage pack for the motors, and converters to step down to 5V for the computer and sensors. Always connect all grounds together.
Safety, seriously
LiPos can catch fire if abused. The rules:
- Use a balance charger made for LiPo. Never charge them with a random supply.
- Never over-discharge. Do not run a cell below ~3.3V. Many robots stop when voltage drops.
- Charge and store in a fireproof bag, and never leave charging unattended.
- Never puncture or bend a pack. A swollen LiPo is retired immediately.
The performance trap
As a LiPo drains, its voltage sags, and motors get weaker. A robot tuned on a full battery behaves differently on a half-empty one. Competitive teams always run on freshly charged packs, because the battery quietly changes how the whole robot moves.