LiPo battery safety for RC cars: charging, storage voltage, damage and disposal

TUREFF• •0

Lithium polymer (LiPo) batteries power most modern electric RC cars. They pack a lot of energy into a small, light pack, which is what makes them exciting to drive with. It also means they can catch fire if mistreated, so understanding a few rules is essential before your first charge.

Know the basics

A LiPo pack is made of cells joined together. A 2S pack has two cells in series, a 3S pack three, and so on.
Each cell has a nominal voltage of 3.7V and is full at 4.2V.
Most packs have two leads: a main power lead and a smaller balance lead that connects to each cell.
Read the battery's label and the manufacturer's instructions for its capacity and maximum charge rate.

Charging safely

Use a charger designed for LiPo batteries, set to the LiPo mode and the correct cell count. Never charge a LiPo on a charger meant for another chemistry, such as NiMH.
Balance charge. Plug in the balance lead so the charger keeps every cell at the same voltage. Unbalanced cells are a common cause of damage.
Charge at a sensible rate. Many people charge at 1C, meaning a current equal to the pack's capacity, so a 5000mAh pack at 5A, unless the manufacturer states otherwise.
Never leave a charging LiPo unattended, and never charge overnight.
Charge in a fire-resistant LiPo bag or container, on a non-flammable surface, away from anything that could catch fire.
Let a hot pack cool down after a run before charging it.
Check the charger settings every time, especially if you use packs with different cell counts.
Have a working smoke alarm nearby and know how you would get out if something went wrong.

Storage voltage

LiPo packs do not like being stored full or empty.

If you will not use a pack for more than a few days, bring it to storage voltage, commonly around 3.8V per cell.
Most LiPo chargers have a storage mode that charges or discharges the pack to that level for you.
Store packs in a fire-resistant bag or container in a cool, dry place, away from children and flammable materials.
Never store a pack in a hot car or in direct sunlight.

Avoid over-discharging

Running a LiPo too low damages it. Most electronic speed controllers have a low-voltage cut-off for LiPo; make sure it is switched on.
When the car slows noticeably, stop and let the pack rest.
A pack that has dropped far below its safe minimum may be ruined and should not be charged.

Spotting a damaged pack

Stop using a pack at once if you see any of these:

Swelling or puffing: gas building up inside the cells.
Dents, punctures, split wrapping or a crushed case, often after a crash.
Damaged wires or connectors.
A pack that gets unusually hot when charging or driving.
A cell that will not hold its voltage or balance.

Do not try to charge, puncture or repair a damaged pack. Move it to a safe place, such as a fire-resistant container outdoors and away from anything flammable, and arrange its disposal.

Disposal

Never throw a LiPo in household rubbish. Batteries in bin lorries and waste sites can start fires.
Cover the connectors with tape so they cannot short.
Take it to a battery recycling point, such as a household waste recycling centre or a retailer that accepts batteries.
Rules vary by area, so check your local council or retailer for what they accept, especially for damaged or swollen packs.

Transport and everyday habits

Carry packs in a fire-resistant bag or hard case, not loose in a bag.
Unplug the battery from the car as soon as you finish driving.
Label packs with dates so you know their age and history.

LiPo batteries are safe to use when treated with respect. What safety routine do you follow? Share your tips or questions in the comments.