How to charge, store and dispose of LiPo batteries

Lithium polymer batteries, LiPos for short, are light, deliver high currents and store a lot of energy in a small space. That is exactly why they need careful handling: follow a few rules when charging, driving and storing, and your packs will last long and stay safe.

The key voltages

A LiPo pack consists of one or more cells in series. The number before the “S” tells you how many: a 2S pack has two cells and a nominal 7.4 V, a 3S pack three cells and 11.1 V. All limits apply per cell:

While you drive, the voltage drops much lower for short moments under load. The low-voltage cutoff of your ESC protects against that, so make sure the battery type is set to LiPo there (more in the guide Brushless motor and ESC). It is even kinder to the pack to stop as soon as the model noticeably loses power: if the resting voltage is then about 3.75 V per cell, you have used roughly 80% of the capacity.

Charging a LiPo: balance lead, 1C and charging time

• Only with a LiPo charger and balancer. Charge LiPos only with a charger that supports the LiPo battery type, and always plug in the balance lead as well as the main lead. The balancer monitors and equalises every cell; without it, one cell can be overcharged even though the total voltage looks right.

• Check the cell count. Before you start, check that the charger shows the correct number of cells.

• Charge current: 1C is the standard. 1C means: charge current in amps = capacity in amp-hours. A 5000 mAh pack is charged at 5.0 A, a 2200 mAh pack at 2.2 A. Use higher rates only if the manufacturer explicitly states them on the pack.

• Charging time. At 1C, an empty pack is full after a little over an hour. Once the cells reach 4.20 V, the charger holds that voltage and the current slowly drops. When it falls below a threshold, the charger reports “full”.

• Charge at room temperature. A pack straight from a run must cool down first; one from a cold car must warm up to room temperature first.

• Safe place, never unattended. Charge on a non-flammable surface, away from anything that burns, never unattended and never inside the model.

The simple USB charging cables that come with many ready-to-run models charge slowly and have no storage function. A charger with balancer, adjustable current and storage function pays off by the time you buy your second pack.

Storing a LiPo: the right storage voltage

If you will not use a pack for more than a few days, bring it to storage voltage: 3.80 to 3.85 V per cell, roughly half charged. Stored full, a LiPo ages much faster and can swell; stored empty, it risks over-discharge. Practically every modern LiPo charger has a storage function that charges or discharges the pack as needed.

How to store correctly:

• cool and dry, ideally at about 10 to 20 °C and out of direct sunlight, so not in the car and not next to a radiator;

• in a LiPo safety bag or a metal container on a non-flammable surface;

• unplugged, never inside the model and never on the charger;

• check the voltage every one to two months, for example with a battery checker, and bring it back to storage voltage if needed.

Storing LiPo batteries over winter

The same rules apply to the winter break. Bring every pack to storage voltage first and keep them frost-free and dry. An unheated garage with sub-zero temperatures and condensation is not a good place. Before the first run in spring, let the packs reach room temperature and then charge them fully as usual.

Warning signs: when to retire a pack

After a full-throttle run, a pack may be warm. If it gets so hot that you can hardly touch it, it is overloaded: its current rating does not match the drive, or the gearing is too tall (see the guide How to calculate RC gear ratio). Take a pack out of service immediately if it

• is swollen,

• has a damaged wrap, dents or chafed wires,

• is deformed after a crash,

• gets unusually hot or smells strange,

• has a cell below about 3.0 V at rest.

Do not charge such a pack again. Put it in a LiPo safety bag, away from flammable material, and take it to a collection point soon.

Disposing of LiPo batteries: not in household waste

Spent LiPos belong at a collection point, such as your municipal recycling centre (in Austria the Altstoffsammelzentrum, in Germany the Wertstoffhof). Not every collection point accepts larger packs over about 500 g; ask beforehand or return them to a retailer that sells such batteries. In Switzerland, every shop that sells batteries takes old ones back. Small packs can also go into the battery collection boxes in shops. First tape over the contacts of the main and balance connectors so that no short circuit can occur. Damaged or swollen packs do not belong in the collection box in a shop: take them directly to the collection point and point out the damage there.

Choosing the right pack

• Cell count (S): must match the ESC and the model. It is stated in the manual, for example “2S–3S”.

• Capacity (mAh): determines run time. More capacity usually also means more weight and larger dimensions.

• Dimensions: measure the battery compartment: length, width and height. Hard-case packs, whose shell protects the cells, are standard in RC cars.

• Connector: XT60, T-plug, XT90 or EC5, matching your ESC. Soldering the right connector on once is better than running with adapters permanently.

• Current rating (C rating): a 5000 mAh pack rated 50C can in theory deliver up to 250 A. The stronger the drive, the more reserve the pack should have.

You will find a large selection among our LiPo batteries.

In short

• Charge only with a LiPo charger and the balance lead connected; the standard is 1C.

• Never charge unattended or inside the model, always on a non-flammable surface.

• Full: 4.20 V per cell. Storage: 3.80–3.85 V. Never below about 3.0 V.

• Let packs cool down after a run and warm up to room temperature before charging.

• Bring unused packs to storage voltage straight away and store them cool, dry and frost-free.

• Do not charge swollen or damaged packs again; dispose of them.