Ryobi battery dead

[Robmoo]

I have a Ryobi One+ 4ah battery pack that is just out of warranty that has died. It had a 4 cell block that was just below 1v. I pulled out the scientific power supply and charged those cells to 3.94v which is what the other cells were at. The lights all still flash and it come up as defective. Do I have a dead BMS? I'd appreciate any insight into this issue. I've watch a few videos and they all deal with dead cells or a battery with an over-all low voltage, but none of those issues is quite what I've got.

 

[mindless1]

I'm not clear on what you mean by a "4 cell block". It is constructed as 5S2P, so I don't see how to consider there being any 4 cell block, and the only way any cell would be below 1V is if it is both defective, and the second series cell in parallel with it is also defective, but both to be that low when the other cells in the pack haven't drained down to less than 3.94V. Even if one of the two cells in parallel were completely dead, then if the other cell in parallel wasn't also weak, before the pair in parallel had drained to 1V, the other cells in the series would have had to drain to no more than 1/2 their total capacity which would be around 3.6V.

After you charge the questionable cells to 3.94V, how long did you wait to try using the Ryobi charger? Is it possible they reached that voltage but then could not hold that charge, then quickly dropped in voltage?

Generalizing, if there is something wrong with the BMS board then it is usually one of the mosfets blown. I have a few Ryobi 4Ah packs but have not had any of them fail, so haven't opened them to become more familiar with that BMS design.

I don't suppose you have a 2nd charger to test, but I do assume that after you charged all cells needing it up to 3.94V, that tools wouldn't run and you get no voltage reading on the battery stem contacts? If not and the cells are all still at 3.94V then yes the BMS has failed, but i still wonder if the pack is about shot for any combination of cells to be down around 1V. How many recharge cycles on this battery?

 

[Red Squirrel]

Since that one cell was down so low, it's probably toast anyway, that cell will always be the weakest link. I would repurpose the working cells for something else (flashlights or some other project) and write off this pack. Although you could try to buy an individual cell that matches and replace it then try again.

I seem to recall reading something to the effect that some power tool batteries essentially disable themselves if they detect any sort of tampering though... I don't know if Ryobi does this or not but it's something to consider as a possibility if you can't get it to work despite having good voltage readings.

I am leaning towards BMS failure though, as that cell would have never been allowed to go that low with a working BMS.

 

[Robmoo]

I'm not clear on what you mean by a "4 cell block". It is constructed as 5S2P, so I don't see how to consider there being any 4 cell block, and the only way any cell would be below 1V is if it is both defective, and the second series cell in parallel with it is also defective, but both to be that low when the other cells in the pack haven't drained down to less than 3.94V. Even if one of the two cells in parallel were completely dead, then if the other cell in parallel wasn't also weak, before the pair in parallel had drained to 1V, the other cells in the series would have had to drain to no more than 1/2 their total capacity which would be around 3.6V.

After you charge the questionable cells to 3.94V, how long did you wait to try using the Ryobi charger? Is it possible they reached that voltage but then could not hold that charge, then quickly dropped in voltage?

Generalizing, if there is something wrong with the BMS board then it is usually one of the mosfets blown. I have a few Ryobi 4Ah packs but have not had any of them fail, so haven't opened them to become more familiar with that BMS design.

I don't suppose you have a 2nd charger to test, but I do assume that after you charged all cells needing it up to 3.94V, that tools wouldn't run and you get no voltage reading on the battery stem contacts? If not and the cells are all still at 3.94V then yes the BMS has failed, but i still wonder if the pack is about shot for any combination of cells to be down around 1V. How many recharge cycles on this battery?

There are 10 cells total, 2 are up front, then a group of 4 and then another group of 4. The 4 in the back were all low, 0.9v. After being connected to my power supply they charged up to 3.94v but the pack still wouldn't work. When I check the voltage of the pack it is 19.94V. The pack should work. There is something there that I'm not educated on and/or am not recognizing.

 

[Tech Junky]

something there

Having let 2 packs sit for too long I ran into something like this and just bought a better battery off Amazon instead of messing with it after they failed to reset and charge.

I think when it comes to these disposable batteries there might be a "fuse" or something that blows when they hit a certain level and disables them from working for safety purposes. On my scanner though they just bloat and expand so they don't fit inside the battery compartment. The scanner batteries though are more expensive at ~$60 for something the size of a Zippo.

I did manage to recover a car battery using a trickle charger similar to what you're using for this. I did go ahead and replace that battery with a new battery since it was pushing a decade in age anyway.

I mean for ~$20 on Amazon it seems like a decent trade off rather than pulling your hair out over a battery. The other option might be to use some jumpers and connect it to another source. I run some stuff off battery banks that typically need to be plugged into AC. Works well but, they're stationary things like a 5G modem for internet or laptop being used in the car for diagnostics.

 

[mindless1]

There are 10 cells total, 2 are up front, then a group of 4 and then another group of 4. The 4 in the back were all low, 0.9v. After being connected to my power supply they charged up to 3.94v but the pack still wouldn't work. When I check the voltage of the pack it is 19.94V. The pack should work. There is something there that I'm not educated on and/or am not recognizing.

It could be that the BMS has locked out use, and I can't blame it because if cells when down to 1V, it could be a fire hazard to continue using it or even to have risked charging it the way you did.

However if you want to live on the edge, see this topic about the possibility of a reset pad you can jumper to ground:

https://www.reddit.com/r/ryobi/comments/y0pon5/ryobi_p189_15ah_bms_reset_success

Personally I would just put the battery pack in a fire proof metal enclosure till I transported it to a recycling center. Resetting it doesn't fix the original problem that put it in this state.

 

[Sukhoi]

It's amazing how willing people are to measurably risk burning down their houses to save a few bucks.