Cracked open my scooter's battery bay today and got a wake-up call

Same thing happened to my e-bike pack last summer. The downtube pack started taking way longer to charge than the usual two and a half hours, then one day it felt warm to the touch an hour after I'd unplugged it. Pulled it out and one corner had gone hard as a brick. Still worked, wich is the part that gets me, because I'd been leaning it against the wall by the back door like an idiot for months before that caught my attention. I took it to a battery shop rather than messing with it myself. The guy there told me a puffed cell can go off with barely any warning and to never squeeze or stack anything on top of it, which I hadn't been doing but the frame itself was doing plenty of squeezing on its own.

The timer idea is a good one. I went with a cheap smart plug set to cut power after three hours, and I only charge out in the garage on the concrete now. Cheap replacement packs from auction sites are what got me into this mess the first time, so I paid up for one with a proper BMS this round. Costs more upfront but I sleep better, and honestly the range has been better too.

Reading this hit close to home because I did the monthly eyeball routine for a while after my own scare and honestly it wore me out. Lifting a deck, peeling back foam, squinting at cases for dents, it got old fast and I know I'd miss something subtle anyway. What actually stuck for me was changing where and when I charge instead of trying to catch a bad cell by sight. I picked up a big metal ammo can from the surplus store, drilled a hole in the lid for the cable, and now anything with lithium in it charges in that can, sitting on a paver slab out in the detached garage. If a pack ever does let go, it lets go in a steel box instead of next to my kid's bike helmets. Costs almost nothing and I don't have to be vigilant about it.

The other thing I changed was trusting charge time as my early warning. My old pack went from about four hours to six over a couple months and I shrugged it off, same mistake you made thinking slow charging was just age. Now if a charge time drifts, that pack goes on the suspicious pile and gets cycled separately til I decide its fate. For what it's worth, your call to toss all three togehter is right even though it stings. Once one swells hard enough to dent its neighbors, those dents are internal damage you can't inspect from the outside.

Before you write those old cells off as the whole problem, check the charger too. I blamed two scooter packs for swelling before I finally put a meter on my stock charger and realized it was running high. Swapped in a proper one and the replacement pack has stayed flat for two years now. Also, don't just toss the puffed one in the trash, my local hardware store takes old lithium packs for free and it took me five minutes to drop off.

One thing I'd add is to write the purchase date on the new packs with a paint pen somewhere you'll actually see it. I started doing that after a weed trimmer pack swelled on me, because it turns out I had no idea wheather it was two years old or five, and age matters more than cycle count for packs that sit around half the year. Also let the garage air out for a few days before you put the replacements in that spot, since that sweet-chemical smell from a vented cell soaks into foam and lingers way longer than you'd expect.

Update: put a meter on my charger after reading that comment and yep, it's running hot. Ordered a proper replacement and the new packs are in, purchase date written on the cases in paint pen like suggested. Still stuck on one thing though, the old swollen one is sitting out in the garage in a metal bucket waiting for disposal day and I keep second-guessing that. Can you just drop these at a regular battery recycling spot, or do they need somewhere special once they've puffed up?