Ryobi 36V (aka 40V) 6Ah Faulty Battery Pack

[brispuss]

Purchased a Ryobi 36V 6Ah battery pack maybe just over a year ago.

Battery pack had been used on about 3 or 4 occasions for powering a cordless lawnmower. I was wanting to use this battery pack again recently, but on checking the battery charge state via the battery pack test button, there was no LED indication at all of charge state which suggested the pack was fully discharged.

I found this to be odd as I usually fully recharge battery packs shortly after use. So either the pack developed some sort of fault which completely discharged the pack cells (after recharging), or I might have forgotten to recharge the pack after last use?

I measured the voltage at the battery pack terminals, 0V!!

On putting the pack into the Ryobi charger, the pack didn't charge and charger displayed alternating green and red LED colors which (according to the charger) suggest pack is faulty.

These battery packs are supposed to have a 3 year warranty, but the problem is I no longer have the sales receipt for the pack. So I can't prove that I purchased it and therefore can't exchange this pack for a new one.

On searching the internet and watching some YouTube videos, I decided to open the pack up and see if I could get this pack to function again.

After removing battery pack bottom cover I measured voltage again, but this time with the negative test lead measuring off the negative solder pad on the pack circuit board, and the positive test lead measuring off the pack positive terminal. This time I measured about 1.7V! So the cells still had a bit of charge still left on them.

I connected a negative power lead to the negative solder pad on the pack circuit board and a positive power lead to the pack positive terminal from a bench power supply set at 36V and current limited to 0.5A.

After an hour plus of "recharging" the pack cells via the bench power supply, the pack cell voltage did rise and reached about 34.5V before I stopped recharging. I again measured pack voltage via pack negative solder pad and pack positive terminal, voltage was about 34.5V. So that looked promising as it suggested the cells were accepting charge OK.

But I then measured pack voltage via the battery pack main terminals, and the voltage was initially around 20V but then started to drop off rapidly!?

I tried testing the pack charge status again by pressing a small test button on the pack circuit board, but no LED's lit up!??

I tried to "reset" the BMS (Battery Management System) by using a jumper from the "RESET" hole on the pack circuit board to the "GND" hole on the pack circuit board, but nothing seemed to have happened with the same voltages as before. Jumper 'trick' was as per suggestions on internet.

Tried to recharge the pack in the Ryobi charger, but once again the pack didn't charge, and again got alternating red and green light LED's flashing suggesting faulty pack.

As the pack cells seem to accept charge, it seems unlikely they are faulty. So maybe there is a fault on the battery pack circuit board?

Maybe I haven't charged the cells enough for the charge status LED's to indicate and also for the Ryobi charger to start recharging this pack?

Maybe I didn't "reset" the pack properly by shorting/grounding the wrong holes on the pack circuit board?

Here are a couple of photos of the battery pack circuit board with annotations.





Any ideas on what is wrong and/or what to try next?

Thank you!

[stj]

Re: Ryobi 36V (aka 40V) 6Ah Faulty Battery Pack

thats not reset, it's a programming connector for the microcontroller

[CapLeaker]

Re: Ryobi 36V (aka 40V) 6Ah Faulty Battery Pack

I think you try to charge the battery as a pack, rather than individual. My guess is that the cells aren’t balanced and you got still a bad cell in there somewhere.

[eccerr0r]

Re: Ryobi 36V (aka 40V) 6Ah Faulty Battery Pack

Dang they should warrant li-ion battery packs for at least 2 years...
1 year really does not cover Li-ion balancing circuitry, alas it does cover their @$$ on lead acid battery mistreatment...

but do check each individual cell for voltage to see if there are any imbalanced cells, alas, probably not much can be done if this is the case. Weak cells are kind of tricky to replace without a welder...

[CapLeaker]

Re: Ryobi 36V (aka 40V) 6Ah Faulty Battery Pack

Forgot to mention, you may have charged the battery, but left it in the tool or mower. Some devices do actually drain the battery if it's left inside.

[sam_sam_sam]

Re: Ryobi 36V (aka 40V) 6Ah Faulty Battery Pack

There is an issue with these battery packs and it not exactly clear what the issue because I have had to return several under warranty so I have not taken one part yet but my warranty has expired on them now and if I have another failure issues with them I will post what I have found

But from what I noticed in one I bought on eBay that was defective was that most of the batteries were bad cells but the question I have is did the BMS protection board failure which caused this or is it batteries that were rejected for some reason and this is what was used

Because the 18 volt battery packs use the same exact battery cells and do not seem to have this issue

Here is my suggestion with your battery pack test each battery cell and if the voltage is below 1.0 be very careful trying to charge these cells because when they become this low on voltage they are very prone to overheating or just will not hold a charge [ maximum charging current should not be more than 200 milliamperes if the battery voltage is below 2.0 volts ] bring the battery voltage back to 3.something but not more than 3.6 volts because you might not be able to wake up the BMS protection board

Or

( the use of a battery testing machine would be very helpful doing this like a SkyRc battery tester which is very useful for this which can be bought from EBay )

One note on unbalanced battery cells you can sometimes rebalancing them but I caution you how to do this
You have to have a way to monitor the battery voltage while discharging them you need to bring each battery cell down to the same voltage but do not go below 2.8 volts

Then

For the BMS protection board to come back to life if it not defective is that the voltage is at least 2.5 to 3.0 volts but the voltage on each battery cell needs to be as close to each other as you can get them

You do have to put the battery pack on the battery charger to wake up the BMS protection board if it does not respond to this then the BMS protection board has issues that might not be able to repair correctly or not

The battery cells that can hold a charge and can be discharged and the amp hours are very close to each other can be reused if you have a battery spot welder that can be bought on eBay if you are interested in doing this I can give you a website link to a decent battery spot welder

I hope this helps

[brispuss]

Re: Ryobi 36V (aka 40V) 6Ah Faulty Battery Pack

All comments noted, thanks!

So the five inline holes marked from SWDIO down to GND is the interface for programming the microcontroller.

As mentioned in my initial post, there are no other "RESET" markings apart from the RESET hole within the 5 inline holes (for programming). Also there is no "RST" marking on this circuit board anywhere for specifically resetting the BMS. Some Ryobi battery pack circuit boards do have a "RST" hole together with an adjacent hole (which may not be marked) in which jumping those two holes would reset the battery pack BMS.

So it appears the only way to "reset" the BMS on this circuit board is to reload firmware into the microcontroller via the 5 hole interface? If so, that means most end users can't do that as they won't have the appropriate firmware, equipment and skills to carry out this task!

Checking each individual cell is not really an option (at this time) as this would require considerable amount of disassembly of the actual cell pack, including removing spot welded cell connections (I believe)! Even if I manage to completely disassemble the cell pack and perhaps find one or more faulty cells, how would I replace these cells? The replacement cells would have to be the same size physically, have the same electrical ratings as the existing cells, and the cells would have to have (presumably) spot welded connections again. I don't have spot welding equipment so proper/reliable cell connections may not be possible(?)

Note that the warranty on this battery pack is 3 years, as mentioned in my first post. But, again, I don't have my sales receipt for this pack anymore and the pack has been opened by myself for attempted repair, so I can't replace this pack under warranty even though I've only had this pack for about a year.

So at this time, full disassembly of the cell pack may not be worth the effort to check each cell individually. And reassembly of the cell pack would be quite difficult I believe, especially if requiring spot welded connections.

Even if I successfully replace any faulty cells and reassemble the cell pack, there may still be an issue with the BMS which may have to be "reset". But resetting the BMS for this circuit board appears to require the use of a programming device (which I don't have) with appropriate firmware (which I doubt I can get hold of anyway).

Looks more likely I'll wind up throwing this pack out!

[jiroy]

Re: Ryobi 36V (aka 40V) 6Ah Faulty Battery Pack

The problem with Li-Ion batteries is , they shouldn't be drained totally . Any device using them , would consider their emptiness drainage to app. 25% .. For example , when a laptop indicate battery is 0% , it means he won't let you use the remaining power .

The problem would aggravate , if , for any reason , or mostly not being used for a longtime , when the emptiness drainage is a real zero .

When I trade with new batteries , i always get sure it's charged to at least 50%.

[brispuss]

Re: Ryobi 36V (aka 40V) 6Ah Faulty Battery Pack

I forgot to add that the battery pack voltage as measured via the negative PCB pad and the positive pack terminal has now reduced to only 2V !!!?? Initial charge voltage was around 34.5V yesterday. So there seems to be some serious discharging going on inside this battery pack!

[sam_sam_sam]

Re: Ryobi 36V (aka 40V) 6Ah Faulty Battery Pack

The issue is that if a battery cell is out of balance enough it turns off the BMS protection board the only way to bring it back to life is to rebalance the battery cells to be very close to each to do this you do not need to take the battery packs apart you just need to solder wires to one cell bank at a time and have each battery cell bank have roughly the same voltage somewhere between 2.8 to 3.5 volts the most important thing to have each battery bank of cells to have the same voltage with in 0.25 volts of each other or better

I have done this many times before and it works as long as the BMS protection board is not faulty or you can not wake up the BMS protection board

The challenge is to remove the battery cells from the battery pack enclosure you need to use plastic tools to gently pry them out of the case because sometimes they are glued in place

[brispuss]

Re: Ryobi 36V (aka 40V) 6Ah Faulty Battery Pack

Thanks for the detailed comments!

This battery pack is now pulled to pieces (beyond repair) since last night!

I decided to remove all of the packs cells and measure their individual voltage. Problem was the cells were well "hidden" within the plastic enclosures (holders) and with conductive metal strips spot welded to each end of the cells. So in order to remove the cells, I had to literally rip off the metal strips and unscrew and tear off parts of the plastic cell holders. In the process of doing all of this the PCB was (partly intentionally) damaged in order to access various parts.

If someone were to attempt to replace cells in a similar battery pack and without (permanently) damaging the battery pack in the process, this would be a very difficult, if not impossible, task!

The 30 cells used within pack are "EVE" brand, 18650 size and rated at 2.0Ah each.



I measured the voltage of each cell with the result of about six of the cells were at ~ 0.3V, one at ~ 0.4V, 8 at ~ 0.5V, 7 at ~ 0.6V, 2 at ~ 0.65V, 3 at ~ 0.7V, and 3 at ~ 0.9V.

But what is not clear, is what was causing the rapid discharge of the cells?

[eccerr0r]

Re: Ryobi 36V (aka 40V) 6Ah Faulty Battery Pack

the protection board itself uses power, but most likely either you had bad cells that killed themselves or left in some sort of drain condition...

[sam_sam_sam]

Re: Ryobi 36V (aka 40V) 6Ah Faulty Battery Pack

Those battery cells are an off brand battery manufacturer so I am not surprised by them being bad or a BMS protection board failure of some type