LiPo packs are why modern bashers are so fast, and they deserve the same respect you give a gas can. Most of the time nothing happens. The goal of this card is to keep it that way. It is not a full battery course (our batteries section covers chemistry, C ratings and choosing packs). It is the short list we want taped to the wall above every charger.
Print it, screenshot it or read it once a month. The numbers come from Battery University, Horizon Hobby's LiPo battery guide, and the ARRMA and Traxxas manuals. The rules about where and how to charge come from years of looking at puffy, melted packs on our repair bench.
The Short Answer
Charge LiPos only on a LiPo balance charger set to the right cell count, inside a fire-resistant bag or box on a hard surface, never unattended, and never if the pack is swollen, damaged or still hot from a run. Stop at 4.2 volts per cell, and store packs at about half charge (roughly 3.8 volts per cell).
- Before: inspect the pack, let it cool, confirm LiPo mode and cell count, plug in the balance lead.
- During: stay close, use a fire-resistant container, keep flammables away.
- After: unplug when done, store at storage voltage, keep packs out of hot cars.
- Puffy pack? Stop using it and do not charge it.
1. Before You Plug In: The 60-Second Pack Check
Most charging problems start with a pack that should not have been charged at all. Run through this card every time. It takes a minute.
| Check | Good | Stop if |
|---|---|---|
| Pack shape | Flat, firm, no puff | Swollen, soft or bulging |
| Wrapper and wires | Intact, no cuts or exposed metal | Torn wrap, nicked wires, melted plugs |
| Temperature | Cool to the touch | Warm from a run (let it cool first) |
| Per-cell voltage | Cells within a few hundredths of a volt | One cell far below the others |
| Charger settings | LiPo mode, correct cell count, balance lead plugged in | Wrong chemistry or cell count shown |
| Location | Fire-resistant bag or box, hard surface, nothing flammable nearby | Carpet, couch, car seat, bedroom |
Swollen means done
LiPo cells live in soft pouches, so when gas builds up inside they puff visibly. Horizon Hobby is blunt about it: "A battery that has ballooned or swollen even a small amount must be removed from service completely." Do not charge it, do not run it and do not poke it. Set it aside somewhere non-flammable and bring it in so we can point you to safe disposal.
Let it cool
Packs and electronics get hot during a run; the ARRMA manual even warns that the ESC heat-sink may be hot after use. Horizon's LiPo guide says a pack must cool to ambient temperature after discharging, so a hot pack should never go straight on the charger. Twenty to thirty minutes is our habit.
Check the cells
A simple cell checker shows the voltage of each cell. They should be close to each other. One cell far lower than the rest points to a damaged or worn cell, and a balance charger will not fix that.
2. While It Charges: Setup and Supervision
Charging is when LiPos are most likely to have problems. Horizon's guide puts it plainly: "Never charge the battery unattended," and charge in an open area away from, and not placed on, anything flammable. Here is the setup we use.
The charging checklist
- Use a LiPo balance charger. Never use a NiMH-only charger on a LiPo.
- Set LiPo mode and the correct cell count. If the charger detects the cell count, confirm it matches the label.
- Plug in the balance lead so the charger can bring every cell to the same voltage.
- Set the charge current no higher than the pack label allows. Horizon's LiPo guide says never to exceed 1C, which is 5 amps for a 5000mAh pack, and 1C is our default.
- Charge in a fire-resistant LiPo bag or box on a hard, non-flammable surface. ARRMA lists a LiPo charging bag as required equipment for its 6S trucks.
- Stay with it. Never charge overnight, while you are out, or in a running car.
- Stop at full. 4.2 volts per cell is full. Battery University says lithium cells "cannot absorb overcharge," so the charger must cut off when full.
Temperature limits
Battery University advises charging at moderate temperature and says "Do not charge at freezing temperature." In a Georgia summer the bigger risk is heat. Battery University treats anything above 30°C (86°F) as elevated temperature, and says the worst situation is keeping a fully charged battery hot. Charge indoors, out of direct sun.
If something goes wrong
Horizon's guide says that if a pack swells while charging, quickly and safely disconnect it, move it to a safe, open area and watch it for at least 15 minutes. If a pack hisses, smokes or catches fire, do not try to handle it: get people and pets away, get out and call 911.
3. After Charging: Storage, Travel and Disposal
The other half of LiPo safety happens when the truck is not running. These habits make packs last longer and keep them safer.
Store at storage voltage
Do not leave LiPos sitting fully charged. Battery University says a lithium cell should not stay at the 4.20-volt ceiling for long, and its estimates show a cell stored a year at 25°C keeps about 96 percent of its capacity at 40 percent charge, versus about 80 percent when stored full. Horizon's LiPo guide notes that a LiPo cell is about 50 percent charged at 3.8 volts and recommends storing at about half charge. Most hobby chargers have a storage mode that does this for you. Use it if you will not run the pack within a couple of days.
Hot cars and garages
Horizon's guide says not to store LiPos in a car or direct sunlight and gives about 40 to 120°F as the storage and transport range. A closed car in a Georgia summer can blow past that. Keep packs out of the car, the trunk and sunny garage shelves, and store them in a fire-resistant container somewhere cool and dry.
Wet and damaged packs
The ARRMA manual says to take caution using LiPos in wet conditions and to check with the battery manufacturer first. After a crash, inspect the pack before charging. Any dent, puncture or torn wrap means retire it.
Run-time habits that help
Keep the ESC's low-voltage cutoff turned on. Traxxas, for example, lists two-stage low-voltage detection on its XL-5 ESC. Over-discharging a pack damages it, and a damaged pack is the one that causes trouble on the next charge.
Conclusion
LiPo safety comes down to a few habits: inspect, cool down, set the charger right, charge in a fire-resistant container where you can see it, stop at full, and store at storage voltage away from heat. Do those every time and you have covered most of the risk.
Need a charging bag or box, a cell checker or a charger that matches your packs? Browse our LiPo safety gear and LiPo batteries, or bring a questionable pack to our Cumming showroom and we will take a look. You can also contact the shop about safe disposal.
Gear Mentioned in This Guide
Bat-Safe LiPo Battery Charging Safe Box
A metal charging box for LiPo packs. Charge inside it, on a hard surface.
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Bat-Safe XL LiPo Charging Safe Box
The bigger version, for 1/8-scale packs or charging more than one at a time.
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Spektrum Smart Battery Checker & Servo Driver
Checks per-cell voltage so you can spot a bad cell before you charge.
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Traxxas EZ-Peak Live 100W Charger with iD (2971)
A LiPo/NiMH balance charger that recognizes Traxxas iD packs automatically.
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Spektrum Smart G2 S1100 AC Charger, 1x100W
A single-port smart charger that reads Spektrum Smart pack data.
Shop nowFrequently Asked Questions
Can I charge a LiPo battery overnight?
No. Never leave a charging LiPo unattended, including overnight or while you are out. Charge it in a fire-resistant bag or box on a hard surface where you can see it, and unplug it when it is done.
What voltage is a fully charged LiPo cell?
4.2 volts per cell. That is 8.4 volts for a 2S pack, 12.6 volts for 3S and 25.2 volts for 6S. A LiPo charger in LiPo mode stops at that voltage; never try to charge past it.
What is LiPo storage voltage?
About half charge, which Horizon Hobby's LiPo guide puts at roughly 3.8 volts per cell. Most hobby chargers have a storage mode that charges or discharges the pack to this level.
Is it safe to charge a puffy LiPo?
No. Swelling means the pack has been stressed or damaged. Stop using it, do not charge it, keep it in a fire-resistant container away from anything flammable, and dispose of it properly.
Do I really need a LiPo bag or safe?
Yes. It is cheap protection if a pack fails while charging. Some manufacturers, including ARRMA for its 6S trucks, list a LiPo charging bag as required equipment.
Can I leave LiPo batteries in my car?
Avoid it, especially in summer. Heat speeds up battery aging, and a full pack in a hot car is the worst combination. Store packs indoors in a cool, dry place inside a fire-resistant container.
