How I care for RC LiPo packs: the five rules that prevent fires, storage voltage at 3.8V per cell, safe charge rates, puffing, and disposing of dead packs.
LiPo packs are the best thing to happen to RC in the last twenty years, and they're also the one part of your car that can burn your garage down. Both of those are true at the same time. Almost nobody actually has a fire, though, and the people who do have usually broken one of the same few rules first.
I've run LiPos in everything from a little 2S Losi Mini to a 6S Arrma Kraton, and I've killed packs by being lazy about all of this. So here's what I do now.
If you skim the rest of this, at least take these:
A LiPo cell is happiest sitting at about 3.8V per cell. That's 7.6V for a 2S pack, 11.4V for a 3S, and so on. Any decent charger has a storage mode that will bring a pack up or down to that number for you.
It matters because a pack left at full charge (4.2V per cell) ages fast. The high voltage stresses the chemistry, and a pack you charged Friday night and didn't run for a month loses real capacity just sitting there. I left a pair of 3S packs topped off in a drawer over a winter and by spring they were puffed and down about a third of their runtime. That wasn't bad batteries, that was me.
So if you charge a pack and don't end up running it, put it back to storage. Leaving it full overnight because you're running tomorrow is fine. It's the weeks that kill them.
Charge rate is measured in C. 1C is a current equal to the pack's capacity, so a 5000mAh pack at 1C is 5 amps. I charge pretty much everything at 1C and only push higher when I'm at the track and need a pack turned around between heats. Plenty of modern packs handle 2C fine, but faster charging runs hotter, and heat is what wears a pack out.
Always balance charge. Plug in the main lead and the little white balance plug, every time. That keeps all the cells at matching voltages, and cells that drift apart are how packs get into trouble. Skipping the balance lead saves you ten seconds and costs you a pack eventually.
The charger matters too. I run a Hobbywing at home and an ISDT for travel, but any modern balance charger from a name you recognize will do. If you're still using the little one that came bundled with a starter kit, that's the first thing I'd upgrade.
Puffing is when a pack swells up. It's gas building inside the cells as the electrolyte breaks down, and it doesn't reverse. A puffed pack stays puffed.
A small puff on an old pack with a lot of cycles on it isn't an emergency, it's the battery telling you it's near the end. You can usually finish out its life gently, storage charging it and keeping an eye on it. But a pack that puffs suddenly, or gets hot in your hand, or won't sit flat anymore, is done. Same goes for any pack you crashed hard enough to dent or poke a hole in. Physical damage to a LiPo is how fires start, and no pack is worth your house.
A LiPo safe bag is the minimum. They're ten bucks and they buy you a lot of margin. I've moved up to a steel ammo can with the gasket cracked open a little so pressure can vent, and it lives on the concrete floor in the garage. The idea is that if a pack does let go, the fire is contained and there's nothing around it to catch.
And again, don't walk away from it. A LiPo fire takes a couple of minutes to develop, so a person in the room is genuinely the best safety gear you own. If you're coming from NiMH and want the background on why these packs need different handling, I wrote up NiMH vs LiPo separately.
The old forum advice was to drop a dead pack in a bucket of salt water for a week. Don't. It corrodes the terminals, it can generate gas, and it doesn't reliably take the cells to zero anyway.
Discharge the pack fully, then recycle it. Some chargers have a discharge function that will take it down low. Otherwise put it in a car and drive it dead, then let it sit and finish going flat. Tape over the leads and take it to a battery recycler. Most hobby shops and the big-box hardware stores have a lithium bin, and Call2Recycle drop-offs are all over the US. Don't put a lithium pack in your household trash.
Treat them right and a decent 3S will give you years and hundreds of cycles. Storage charge, balance charge, don't cook them, don't run them flat. When runtime drops off a cliff or one starts puffing, let it go. A tired pack sagging under load makes a good motor feel gutless and you'll waste a weekend chasing the wrong problem.
Charging habits are only half of it. The same fifteen minutes of post-run maintenance will save you more than it costs. And if you've retired a pack and need a replacement, check the buy/sell listings before you pay retail, since people sell off good packs whenever they downsize. Anything I didn't cover is probably in the FAQ.