LiPo batteries explained: 1S to 6S

What is a LiPo battery?

LiPo stands for lithium polymer. Technically it is a lithium-ion battery, but with flat cells in a soft sealed wrapper (a pouch) instead of a metal can. That makes a LiPo light and able to deliver a lot of current quickly: exactly what an FPV drone needs to accelerate hard.

There are downsides too. A LiPo needs a suitable charger, must not be run too flat, degrades when left fully charged for long, and can swell or catch fire when damaged. How to handle that is covered in charging and storing LiPo batteries safely.

What do 1S, 2S, 3S and 4S mean?

The S stands for series: the number of cells connected one after another. Each extra cell adds its voltage. A standard LiPo cell is 3.7 V nominal and full at 4.20 V; a LiHV (high-voltage) cell is 3.8 V nominal and full at 4.35 V.

• 1S — 3.7 V nominal, 4.20 V full (LiHV: 4.35 V). Common on 65 and 75 mm tiny whoops.
• 2S — 7.4 V nominal, 8.40 V full. More powerful whoops and small toothpicks.
• 3S — 11.1 V nominal, 12.60 V full.
• 4S — 14.8 V nominal, 16.80 V full.
• 6S — 22.2 V nominal, 25.20 V full.

Only use the cell count your drone is built for. A plug that fits does not prove the voltage is right: a 2S pack on a whoop designed only for 1S can damage the electronics.

Capacity (mAh) and C-rating

Capacity in milliamp-hours (mAh) tells you how much charge the pack holds. More mAh does not automatically mean a longer flight: a bigger pack is also heavier, and on a tiny whoop every gram counts.

The C-rating is the manufacturer’s figure for the current a pack can deliver continuously, as a multiple of its capacity. Maximum current = C-rating × capacity in amp-hours. BetaFPV gives the example of a 1S 300 mAh 30C pack: it delivers 9 A continuous. A 270 mAh pack rated 95C works out at just over 25 A.

Do not run a LiPo too flat. BetaFPV names 3.0 V per cell under load as the absolute minimum. Land well before that and set a voltage warning in your OSD so you know in time when the pack is running low.

Connectors: BT2.0, PH2.0 and XT30

Small 1S packs often use a BT2.0 or PH2.0 connector. For PH2.0, BetaFPV states 4.5 A continuous. The two do not fit each other, so check which connector your drone has before buying batteries. Multi-cell packs usually use XT30 or XT60.

Choosing batteries for your whoop? Compare cell count, connector, capacity, weight and size in the batteries category, and read What is a tiny whoop? for why battery and connector both have to match.

LiPo, LiHV and Li-ion: what is the difference?

LiHV is a LiPo that may be charged to 4.35 V per cell instead of 4.20 V. That gives slightly more voltage at the start of a flight. You need a charger that supports the LiHV (4.35 V) setting.

Never charge a standard LiPo to 4.35 V: that is overcharging. Many small 1S whoop chargers charge to a fixed 4.35 V and are therefore only suitable for LiHV packs. Check your charger’s end voltage against the battery type.

Li-ion (such as 18650 and 21700 cells) holds a lot of energy per gram but delivers less current relative to its capacity. A 4.5 Ah 21700 cell, for example, is rated for 45 A continuous (10C), while whoop LiPos are rated at 75C to 95C. That is why Li-ion mostly appears on drones built to cruise for a long time, and LiPo on drones that need to be fast and agile.

How long does a LiPo last?

Mostly on how you use it. What wears a LiPo faster: running it too flat, charging it while still warm, leaving it full for long periods, and crashes. BetaFPV advises not to keep a full pack for more than three days and to hold 3.8 to 3.9 V per cell for longer storage.

Is a pack swollen, deformed or damaged? Stop using it. What to do next is in the guide on swollen LiPo batteries.