How to Fix a Swollen LiPo Battery? You Can’t – Here’s What to Do
You can’t fix a swollen LiPo battery. The swelling is gas from chemical breakdown inside the cells, and it doesn’t go away; poking holes, pressing it flat or “rebalancing” it can start a fire. Stop using the pack, put it in a fireproof container away from anything flammable, and take it to battery recycling or hazardous waste collection. If it is only slightly puffed and not hot, you may discharge it slowly first, but only with a proper discharger. Here’s how to tell how bad it is, what to do, and how to prevent it.
By Kyle HilsonUpdated: October 20264 min read
Why do LiPo batteries swell?
| Cause | What happens |
|---|---|
| Over-discharge (below about 3.0 V per cell under load) | Damages the cell chemistry; the most common cause in RC |
| Overcharging (above 4.20 V per cell for standard LiPo) | Breaks down the electrolyte |
| High current beyond the C rating | Heat builds inside the cells |
| Storing full or empty for weeks | Slow degradation and gas build-up |
| Heat (hot car, sun, right after hard use) | Accelerates breakdown |
| Crash damage or punctures | Internal shorts |
| Age | Packs puff slowly near the end of their life |
How bad is it?
| Condition | What to do |
|---|---|
| Slightly soft or puffy, cool, voltages normal | Retire it. Don’t fly or drive with it; discharge slowly and recycle |
| Clearly swollen, cool | Isolate in a fireproof container; recycle without charging or discharging hard |
| Hot, hissing, smoking or smelling sweet | Move it outdoors onto sand or concrete with tongs if safe, keep away; call emergency services if it catches fire |
| Punctured or leaking | Don’t touch with bare hands; isolate and take to hazardous waste |
How to dispose of a swollen LiPo safely
- Stop charging and using it. Unplug it from the model or charger.
- Isolate it in a LiPo safe bag, metal ammo box (without an airtight seal) or a bucket of sand, outdoors or in a garage away from flammables.
- Watch it for an hour or two for heating or more swelling.
- Discharge only if mildly puffed: use a charger’s discharge function or a dedicated discharger at a low rate (no more than about 0.5C) down to about 2 V per cell. Never discharge a hot, badly swollen or damaged pack.
- Tape the connectors so they can’t short.
- Recycle it: municipal hazardous waste sites, battery drop-off bins at shops, or a locator such as Call2Recycle (US). Never put LiPos in household rubbish.
Saltwater myth: soaking a LiPo in saltwater is often recommended, but the salt corrodes the terminals and wires before the cells are empty. The pack then reads 0 V at the plug while the cells still hold charge. Use a discharger or take it to recycling as it is (HobbyKing and other battery sellers now advise against the saltwater method).
What not to do
- Don’t puncture it to “let the gas out”: air and moisture react with lithium and can ignite.
- Don’t press it flat or squeeze it into a battery tray.
- Don’t charge it “one more time”.
- Don’t store it indoors near anything flammable.
- Don’t throw it in the bin or burn it.
How to prevent swelling
- Keep the ESC’s low-voltage cutoff on and use a timer: land or stop at about 3.7–3.8 V per cell resting.
- Charge with a balance charger at 1C unless the pack is rated higher, and never leave charging packs unattended.
- Store at storage voltage (about 3.8 V per cell) if you won’t use them for more than a few days.
- Let packs cool before charging and after use.
- Choose packs with a C rating comfortably above your model’s current draw.
- Check packs after crashes; retire any with damaged wrapping or dents.
FAQ
Can a swollen LiPo go back to normal?
No. The gas and the internal damage stay. Even if it shrinks a little when cool, the pack is damaged.
Is a slightly puffy LiPo safe to use?
No. Retire it: puffing means the cells are degrading and the risk of failure under load rises.
Can I use a swollen LiPo for storage or low-power use?
Not safely. Recycle it.
Why did my new LiPo swell after one run?
Usually over-discharge (no cutoff), too much current for its C rating, or a defective pack. Contact the seller.
More on this topic: the complete RC Basics guide covers the basics behind this article.
About 20 years in RC. Mostly boats in the NAVIGA Mini Eco Expert class, with many self-made parts; also a King Motor Baja 5B, a home-built electric plane, home-built nitro planes he has flown, and an RC helicopter. More about SwellRC
