LiPo batteries explained

A LiPo label crams a lot into a few characters. Take a typical pack: 3S 1300mAh 45C, XT60. Once you know what each part means, choosing a battery for any model becomes straightforward.

This page explains the numbers and how to use them. How to charge, store and dispose of packs safely is covered separately in LiPo battery safety, and it's worth reading before you charge your first pack.

Reading the label

Cells and voltage: the S number

Each LiPo cell has three voltages that matter:

Packs are made by joining cells in series, which adds their voltages together:

More voltage means the motor spins faster. The cell count your model can use is set by its speed controller and motor, so never fit more cells than the electronics are rated for. Our guide to ESCs and brushless motors explains how voltage and motor kV work together.

Capacity: mAh

Capacity is the size of the fuel tank. A 2200mAh pack holds about twice the energy of a 1100mAh pack of the same voltage, so it runs about twice as long. It is also about twice the weight.

That trade-off matters most in aircraft. A heavier pack makes a plane or helicopter work harder and can upset its balance, so stay within the range the manufacturer recommends. In cars there's more room, and fitting the largest capacity that physically fits is usually fine.

C rating: how much current a pack can deliver

The C rating tells you the maximum continuous current, as a multiple of capacity:

Maximum current (amps) = capacity (Ah) × C rating

So a 1300mAh 45C pack can, on paper, deliver 1.3 × 45 = about 58A. A 5000mAh 50C pack: 5 × 50 = 250A.

Two cautions:

• Labels are often optimistic. Retailers and testers regularly note that real-world C ratings are lower than printed figures, especially on cheaper packs. Treat the number as a rough guide, and compare brands rather than labels.
• Burst ratings are for seconds, not minutes. A "45C/90C" label means 45C continuous, 90C for short bursts.

A higher C rating than you need never hurts. The pack simply runs cooler and holds its voltage better. Too low a rating makes the pack sag, run hot and wear out fast.

LiHV, LiFe and Li-ion

Not every lithium pack is a standard LiPo:

The charger setting must match the chemistry on the label. A LiHV pack charged as a LiPo just won't be full; a LiPo charged as LiHV is overcharged and dangerous.

Connectors

The main plug carries the power. Common ones:

You can use an adapter to try a pack, but for regular use it's better to solder the right plug on. Adapters add resistance and another joint that can work loose. Undersized connectors on high-current models get hot and eventually melt.

The balance lead is separate: a small white JST-XH plug with one more wire than there are cells. It's only used for charging.

Hard case or soft pack?

Cars use hard-case packs: the plastic shell protects the cells from impacts and dirt. Planes and helicopters use soft packs wrapped in heat-shrink, because every gram counts. Never put a soft pack in a car chassis without protection.

Choosing a pack for your model

Micro helicopter (for example a 1S or 2S micro): use the capacity the manufacturer specifies and its connector. Small packs are matched tightly to the model's weight. Higher-quality packs give noticeably better punch.

Foam trainer plane (3S): 3S 2200mAh is the most common size for 1.1 to 1.5m trainers. Check the balance point after fitting a different brand, as weights vary. Our guide to balancing an RC plane shows how.

1/10 car (2S): 2S hard-case, 4000 to 6000mAh, 50C or more for brushless. Make sure the ESC's cut-off is set to LiPo.

Making packs last

• Store at storage voltage whenever you won't use a pack within a couple of days.
• Don't run packs flat. Stop at the first sign of power loss.
• Let packs cool before charging, and charge at 1C.
• Check internal resistance if your charger shows it. A pack whose resistance has risen a lot, or has one cell much higher than the others, is near the end of its life.
• Keep a simple log. Write the purchase date on each pack.

When you're ready to buy a charger, see our best LiPo chargers. If your model came with NiMH batteries, read NiMH vs LiPo before you switch. For RC car batteries specifically, the RC car buyer's guide covers what to buy with a first car. Every electronics guide is listed on the Electronics hub, and battery terms are defined in the RC glossary.