Trying to jump start a dead power tool battery (and failing)

#1 · Jun 7, 2026

Got this older Li-ion Ryobi battery I haven't used for a couple years. Not good, I know, but I'm trying to wake it up to accept a charge from the charger. It does the blinking red/green thing saying the battery is defective or doesn't have enough voltage to use the charger. I checked the voltage and it's way low but there. I tried putting it in and out of the charger 30 or so times to get it to wake up (worked on a Milwaukee battery years ago) — no dice after 20 minutes. So I got these Stihl batteries that I think have the same power and tried jumping off one. Made sure of the polarity with a tester and jumped them for 10 seconds, then put the Ryobi back on the charger — same blinking defective show. Did this twice, no luck. Am I doing the right things? Is the Ryobi toast? Immediately after jumping it reads about 10v then slowly drains down to 3 or so. Is it toast?

#2 · Jun 7, 2026

Sounds like the Ryobi is toast. I've revived tool batteries with just a 9v — it's not jumping per se, just enough residual voltage to engage the charger.

#3 · Jun 7, 2026

Tend to agree on that one — probably too low for too long and internally shorted.

#4 · Jun 7, 2026

Internally shorted… explain please?

#5 · Jun 7, 2026

Probably not the best description — "brick mode" is more like it. Lithium batteries go through a chemical breakdown when the voltage is too low for too long and lose capacitance. They go into brick mode and will never work again. They can short internally, but by then there usually isn't enough voltage left to self-combust. Either way they're dead. I used to race RC cars and have seen batteries catch fire from people trying to jump start them. Never a good idea.

#6 · Jun 7, 2026

OK, first thing: DON'T LISTEN TO ME, and DON'T TRY WHAT I WOULD TRY — do this at your own risk. Your battery may be toast, but being cheap, I'd try to get that residual voltage a bit higher than 10v. Attach the boost source longer, say 20 seconds at first, watching the current so your jumpers don't overheat. Li-ion cells are nominally 3.6–3.7v and ~4.2v charged. Below 2.5v per cell they're considered irreversibly damaged. Li-ion chargers won't charge below a certain level — you have to find what that is for your charger. NEVER charge lithium batteries unattended, and especially when trying to rejuvenate a suspected dead one. Lithium fires are real and can burn your house down.

#7 · Jun 8, 2026

This is not the proper attire to wear while NOT doing what Tomfive said... 🤣

#8 · Jun 8, 2026

Try using a battery tender, which should bring the battery up to 12 volts or more.

#9 · Jun 8, 2026

I have tried to revive a few tool batteries — never worked for me.

#10 · Jun 8, 2026

I have one particular 40V DeWalt battery that I frequently have to "jump" to get it to take a charge if I run it too low. Works every time. But I've also had batteries go to crap that will no longer accept a charge even after trying to jump them.

#11 · Jun 8, 2026

The charger communicates with the battery — the link is established anytime the battery is placed on the charger. Each battery has an on-board controller to monitor over/undervolt, over/undertemp, overcurrent, etc. Not sure if Ryobi does this, but on some Makita batteries, after a few failed charge attempts the on-board controller permanently disables charging.

#12 · Jun 8, 2026

Most name brands are the same way. I hate buying batteries — they're expensive, but not nearly as expensive as burning down your shop messing around with them. I dispose of them when they stop charging; it isn't worth my effort or the risk.

#13 · Jun 8, 2026

I went through this with some DeWalt batteries that wouldn't jump. I came across a video where a guy took them apart and pushed down on the tops of the cells with a small screwdriver — they'd release a little hiss and after that the charger would charge them again. I tried it and it worked, but the batteries ran a few cycles and failed again. I finally decided it wasn't worth the fire risk and replaced them.

#14 · Jun 8, 2026

It's not the end of the world if I toss it, but it's my only battery for a handheld tiller I quit using years ago and I wanted to throw it on Marketplace for a couple bucks or give it away. If I can't get it to take a charge I'll take the whole shebang to the dump. To answer a few comments: I read that Li-ion batteries should NOT be hooked to a trickle charger/tender due to all cells charging at the same time. I took the pack apart — no reset switch, and I'm not poking cells with a screwdriver until they hiss, lol. I might leave them hooked up for 20 seconds to see if it takes a charge, but if not, into the dumpster it goes. Thanks guys.

#15 · Jun 8, 2026

Try this: locate a proper, dedicated power-tool recycle bin. Drop the battery in the bin. Go home and open a cold beer. Enjoy the remainder of your day.

#16 · Jun 8, 2026

One little thing to keep in mind about lithium batteries: when they go up in flames you can't put them out because they make their own oxygen. So you're literally playing with fire. Good luck.