My Milwaukee 5.0Ah battery has started to swell up noticeably and feels warm. I've had it for about 3 years and used it pretty regularly. Should I stop using it immediately or is this something I can still charge and use safely? I'm worried it might explode or catch fire while I'm working.
Stop using it right now and don't charge it - swelling means the internal chemistry is breaking down and lithium batteries can absolutely catch fire or explode when they're in that state, especially under load or heat. Dispose of it properly at an e-waste facility or take it back to where you bought it, since most retailers have battery recycling programs.
The safest move is to store it outside your house in a metal container or toolbox in a garage or shed - away from anything flammable - until you can dispose of it properly through a battery recycling program or your local electronics waste facility. Swollen batteries are unstable and keeping one indoors, even unused, poses a real fire risk.
Get that battery away from your house and anything combustible - swelling combined with warmth is a sign the cells are failing and can self-ignite without warning, even when just sitting there. Don't charge it or use it again; the internal damage is already done. Seal it in a non-metal container (metal can conduct heat) in a shed or garage away from the house, then contact your local recycling center or hazardous waste facility about proper disposal - Milwaukee also runs take-back programs if you want to go that route.
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