LiPo battery safety

Lithium polymer batteries power almost every modern RC helicopter, plane and car because they store a lot of energy in very little weight. That same energy is why they need handling with care. Treated properly, a LiPo is a safe, well-behaved battery that will last a few hundred cycles. Treated carelessly, it can catch fire in a way you cannot put out with a glass of water.

This guide covers the whole life of a pack: charging, using, storing, carrying, and finally getting rid of it. If you want to understand what the numbers on the label mean first, read LiPo batteries explained.

The five rules that prevent most LiPo fires

Almost every LiPo incident I have heard about breaks one of these:

1. Use a proper balance charger, set correctly. The charger must be set to LiPo (or LiHV if the pack says so) and to the right number of cells. A wrong setting is the single most common cause of a fire. The best LiPo chargers all have a balance port and a storage mode.
2. Never charge unattended. Stay in the room while packs are charging. The London Fire Brigade advises against leaving batteries charging overnight or after the charge cycle has finished (London Fire Brigade battery advice).
3. Charge on a non-flammable surface. A ceramic tile, a concrete floor, a metal tray or a purpose-made fire-resistant box. Not the carpet, not the sofa, not a wooden workbench covered in balsa dust.
4. Retire damaged packs. Swollen, dented, punctured or crash-damaged packs do not get charged again.
5. Don't run packs flat. Over-discharging damages the cells and makes the next charge riskier. Land or stop driving when the model first loses punch.

Charging safely

Set the charger correctly every time

Before you press start, check three things on the charger screen: the chemistry (LiPo or LiHV), the cell count, and the charge current.

• Chemistry. A standard LiPo is full at 4.2V per cell. A LiHV pack is full at 4.35V per cell. Charging a standard LiPo on a LiHV setting overcharges it.
• Cell count. A 3S pack has three cells in series. Most chargers detect this through the balance lead, but always confirm it matches the label.
• Charge current. Charge at 1C unless the manufacturer says otherwise. For a 1300mAh pack, 1C is 1.3A; for a 5000mAh pack it is 5A. Horizon Hobby's safety guidance is never to charge above 1C (Horizon battery safety sheet).

Always balance charge

The balance lead (the small white plug with one more wire than the pack has cells) lets the charger watch every cell. Balance charging stops any single cell going over 4.2V, which is where trouble starts. Plug in both the main lead and the balance lead, every time.

Let packs cool down first

A pack straight out of a model is warm. Charging a hot pack shortens its life and adds risk, so let it return to room temperature before you charge it. The same goes the other way: don't charge a pack that has been sitting in a freezing car.

Where to charge

A fire-resistant LiPo bag or a steel ammunition box with the seal removed (so gas can escape) is the minimum. Put it on a non-flammable surface, away from curtains, paper and anything else that would burn. A smoke alarm in the room is cheap insurance.

Using packs in the model

• Mind the low-voltage cut-off. Most car ESCs and helicopter and plane speed controllers can cut or reduce power at a set voltage. Make sure it is set for LiPo, not NiMH. Our guide to ESCs and brushless motors explains how.
• Fly or drive by time, not until it stops. Time a few runs with a timer, then set it to finish while the pack still has around 20% left. Resting voltage after a run should be no lower than about 3.7V per cell.
• Secure the pack. A pack that can slide around in a crash can be punctured by a frame or a screw. Use the straps and hook-and-loop the model came with.
• Check after crashes. After any heavy crash, unplug the pack, look for dents, splits or swelling, and put it somewhere safe for half an hour before charging.

Storage

LiPos last longest and are safest at about half charge. Leave a pack full for weeks and it slowly swells; leave it flat and it can drop below the point it can recover from.

• Storage voltage: about 3.8V to 3.85V per cell. Use your charger's storage mode, which charges or discharges each pack to the right level. Charger manuals typically allow storage settings between 3.75V and 3.90V per cell (SkyRC B6neo manual).
• When to use it. If you won't use a pack within a couple of days, put it to storage charge.
• Where to keep packs. In a fire-resistant box or bag, somewhere cool and dry, away from flammable things. A garage shelf is better than a bedroom.
• Temperature. Avoid extremes. Don't leave packs in a hot car in summer or a freezing shed in winter.

Spotting a damaged pack

Check every pack before you charge it. Retire it if you find any of these:

A pack that is warm after a hard run is normal. A pack too hot to hold comfortably is not.

Carrying LiPos and flying with them

In the car, carry packs at storage voltage in a fire-resistant bag, not loose in the boot.

On a flight, spare lithium batteries must go in your cabin baggage, never in the hold, with the terminals taped or each pack in its own bag. Packs up to 100Wh are generally allowed; between 100Wh and 160Wh you need airline approval and are limited to two; above 160Wh they cannot go as passenger baggage (IATA lithium battery guidance). To work out watt-hours, multiply voltage by capacity in amp-hours: a 3S 2200mAh pack is 11.1V × 2.2Ah, about 24Wh. Always check your airline's own rules before you fly.

Disposing of old LiPos

Never put a LiPo in the household bin or a recycling bin. Lithium batteries crushed in bin lorries and waste plants are a well-known cause of fires.

1. Discharge the pack. Use your charger's discharge mode to take it to its lowest setting. This reduces the energy left in it.
2. Tape the terminals. Cover the main connector and balance plug with insulating tape so they can't short.
3. Take it to a collection point. Shops that sell batteries must take used portable batteries back under the Waste Batteries and Accumulators Regulations (GOV.UK battery regulations), and most household waste recycling centres accept them. Recycle Your Electricals has a postcode search for drop-off points.

For a puffed pack, keep it in a fire-resistant container outdoors or in a garage until you can take it in, and tell the staff it is swollen.

If a LiPo catches fire

• Don't try to grab it. Your hands are worth more than the model.
• If it is contained in a LiPo bag or metal box on a non-flammable surface, keep people back and let it burn out, ventilating the room if you can do so safely.
• If it is spreading, get everyone out, close the door and call 999.
• Don't use water on a burning pack indoors unless you have been trained to. Fire services can advise; it's the reason they recommend charging in a safe place in the first place.
• Afterwards, treat the remains as hazardous and take them to your local waste site.

Children and LiPos

Children's toy-grade models usually come with small LiPos and USB chargers. The same rules apply: an adult should supervise charging, packs should be charged on a hard surface, and any swollen pack goes for recycling. Our guides to the best RC helicopters for kids and best RC cars for kids cover the safest options.

If you're still deciding between battery types, NiMH vs LiPo explains when the older chemistry still makes sense. For everything else electrical in a model, start at the Electronics hub.