My cordless vac won't charge - battery light blinking red

Hey all, I've got a cordless car vac (18V) and the battery won't charge. The charger light just blinks red when I put it on. It's a few years old. Any idea what's wrong? I've tried cleaning contacts and stuff, but no luck.

Blinking red usually means battery is burnt out or the charger can't detect it. If ya got another battery, test the charger. If charger works, then battery's toast. Also, check if the battery is swollen - that's a safety hazard. If so, recycle it properly and get a new one.

Before splashing cash, try jump-starting the battery if it's been sitting dead for a while. I've revived a few by connecting it to a healthy battery for a few seconds (with wires) to give it a kick. But be careful: only do it if you know what you're doing. Otherwise, might be cheaper to get a new battery than a whole vac. I've seen knock-offs on Amazon that work fine.

Also, check the charger's contacts for corrosion. Sometimes the prongs get dirty. But if it's blinking red, that's usually a signal. Try leaving it on charge for a few hours - some chargers blink red if the battery is too hot or cold. Let it cool down to room temp and try again. If not, I'd bet the battery cells are dead. I've had a few batteries go that way after heavy use.