Part of the RC Airplane Troubleshooting Center
If your LiPo battery is puffed or swollen, stop using it and don’t charge it again. That’s a pack I wouldn’t put back in an airplane.
Batteries aren’t cheap. I understand wanting one more flight out of a pack that still takes a charge. But “it still works” doesn’t tell you whether it’s safe. Replacing a battery is a lot better than losing the airplane or having a fire in the shop.
What to Do When You Find a Puffed LiPo
Before worrying about what caused it, deal with the battery you have in front of you.
- Stop using that pack. Don’t try another charge or another flight to see whether it settles down. If it starts swelling on the charger, disconnect the charger’s power only if you can do that safely without approaching a failing battery.
- Leave the testing alone. Don’t keep plugging it into the charger, a cell checker, or the airplane looking for a number that says it’s okay. Don’t squeeze the cells to see how puffy they are, either.
- Keep it away from things that can burn, when safe. Don’t handle a hot or unstable pack. For a cool, stable pack, follow the manufacturer’s handling instructions and keep the connectors from touching metal or other battery terminals.
- Find out who will take it. Call a household hazardous-waste program or a recycler that accepts damaged lithium batteries. Tell them it’s swollen before you show up with it.
Horizon Hobby’s instructions say to stop using swollen or damaged packs. London Fire Brigade’s guidance explains the warning signs that need immediate attention.
Can You Use a Slightly Puffed LiPo Battery?
“It’s only a little puffy” is an easy thing to tell yourself when you’re looking at an expensive battery. I still wouldn’t use that as a reason to keep flying it. A normal voltage reading or a charger that finishes without an error doesn’t make the swelling okay.
There is some nuance here. SMC explains that cells can expand during normal charging and discharging, which is different from a pack ballooning. But that doesn’t give you a useful “this much puffing is fine” rule to use at the field.
If you can’t tell whether the shape is normal for that battery, stop using it and ask the manufacturer. Someone else getting away with flying a questionable pack doesn’t tell you anything about yours.
The battery that keeps going back in the box
We had a conversation in Episode 203, around 1:14:12, about an old Venom pack that kept getting put back in the battery box. Every time getting rid of it came up, it went right back in with everything else. The pack wasn’t puffy, and swelling was specifically mentioned as a reason it would have been gone.
That’s an easy habit to understand. You paid for it, and maybe it still has some use left. But once a pack is swollen, don’t keep moving that decision to the next flying day. Arrange proper disposal.
Why Do LiPo Batteries Puff Up?
The short version is that unwanted reactions inside the cells can produce gas. That gas builds up inside the sealed pouch and makes the pack swell. Electrolyte breakdown is one part of that process; research on pouch-cell aging goes into the details. It isn’t just air under the outer shrink wrap.
Here are the things worth looking back at:
- Charger settings. Was the chemistry right? The cell count? The charge rate? Follow the battery’s limits.
- Heat and current draw. An overloaded pack, poor cooling, or a hot vehicle can be hard on batteries.
- Running it too low. Flying too long, an unsuitable cutoff setting, or leaving the battery connected can over-discharge it.
- Crash damage. A crushed, punctured, or otherwise damaged cell is a reason to stop using the pack.
- Age or an internal problem. Swelling alone doesn’t prove what caused it or that you did something wrong.
Think about how the pack was used so you can avoid repeating a problem with the next one. Don’t run the swollen battery through more tests to figure it out.
Can You Fix or Unpuff a LiPo?
This is one thing I would leave out of the repair pile. Don’t poke a hole in it, squeeze it flat, cut it open, replace cells, or put it in the freezer. Even if it looks smaller later, that doesn’t prove the battery is safe.
Don’t deliberately discharge a swollen pack with salt water, a light bulb, a resistor, the airplane’s motor, or a charger program. Get disposal instructions for the condition it’s in first. Gens ace and Tattu’s instructions say to stop charging or discharging swollen packs and warn against puncturing, disassembling, or soaking cells.
How to Dispose of a Puffed LiPo Battery
This part takes a phone call. In the U.S., contact your local household hazardous-waste program, the manufacturer, or a specialist battery recycler. Tell them: “I have a swollen lithium-polymer RC battery. Do you accept damaged packs, and how should I prepare and transport it?”
Don’t put it in the trash or curbside recycling. And don’t drop it into a battery collection box just because the store accepts batteries. Damaged packs can need a different process, as the battery collection locator explains.
Follow the receiving facility’s directions for packaging, protecting the connectors, and transport. Don’t cut off the leads or mail it without specific instructions from an authorized program. While you’re arranging that, keep a stable pack away from things that can burn and make sure it doesn’t get mistaken for a usable battery.
The EPA has guidance on swollen batteries and disposal. Outside the U.S., check with your local waste authority.
How to Take Better Care of Your Next Pack
We talked about why this matters in Episode 180, around 53:03. One of us described a LiPo failing outside and being right there when it happened. The conversation came straight back to staying nearby while batteries charge.
LiPos are something you can learn to use and care for properly. But getting comfortable with them shouldn’t turn into ignoring the precautions. For healthy, undamaged packs, here’s what I’d focus on:
- Check the charger before pressing Start. Chemistry, cell count, and charge current need to match the pack. Use the manufacturer’s specified balance-charging procedure and stay nearby.
- Give a hot pack time to cool. Wanting another flight doesn’t make it ready for the charger. If it’s getting unusually hot, figure out why.
- Land with some margin. Set a conservative timer and learn what the airplane normally uses. I wouldn’t make low-voltage cutoff the signal to start thinking about landing.
- Use storage charge. If healthy packs are going to sit, follow the manufacturer’s storage instructions. Around 3.8 volts per cell is common. Don’t leave them full or deeply discharged for extended periods, and don’t use storage mode as a way to fix a swollen pack.
- Look at how the battery fits. It needs to stay put without being crushed against a strap or sharp edge. Make sure the installation provides the cooling it needs.
If the same airplane keeps being hard on batteries, I’d look at the setup before putting another pack through it. Check flight time, cooling, charger settings, battery suitability, and what the motor and propeller are asking from the pack. The hot battery or connector guide gives you a place to start. Don’t use the swollen pack for a current-draw test.