How can I test a 40v Li-Ion battery for a Greenworks 25292 cordless mower?

[MowerMike]

It definitely looks like you have a bad battery. Just because the battery charge indicator shows a fully charged battery doesn’t mean the battery is good. I have several batteries that show all charge LEDs on, yet as soon as I put them in a tool and switch it on, it immediately shuts down or doesn’t start at all. It only takes one bad cell in a lithium-ion battery pack to make it fail.

 

[ilyaz]

So is it possible to repair this battery by replacing bad cells? A new battery costs $100+ and that's a lot of money. Hate to throw away a good mower for this reason. If I could repair the battery for much cheaper that would be awesome!

 

[MowerMike]

It is possible, but not easy. Some manufacturers will refurbish batteries, but I don’t think Greenworks does this. I just looked at one of my Greenworks 40 volt Gen1 batteries, and the case is held together with screws with rejection pins, so I looks like they are not meant to be opened for repair. I did open two other dead batteries, and the cells were connected with welded steel strips that I destroyed when I disconnected them from the bad cells, so I gave up trying to repair them. The only other possibility I can think of is to take it to a Batteries + Bulbs store store, and see if they can repair it.

 

[ilyaz]

Well, I took it apart. I did such a fine job that I don't think anyone can put Humpty Dumpty together again... So looks like my only options at this point is to buy a new battery or take the mower apart for spare parts.

 

[1 Lucky Texan]

I think there are 1 or 2 aftermarket compatible units around - dunno about their quality.

check ebay and amazon.

 

[MowerMike]

I think there are 1 or 2 aftermarket compatible units around - dunno about their quality.

check ebay and amazon.

There are a few of them, but they are really expensive now, well over $100, and take over a month to ship from China.

 

[bertsmobile1]

So is it possible to repair this battery by replacing bad cells? A new battery costs $100+ and that's a lot of money. Hate to throw away a good mower for this reason. If I could repair the battery for much cheaper that would be awesome!

Yes and no.
The battery is made up of individual 3V cells.
They are very easily damaged by excessive heat so you need a big soldering iron that will heat the region where the cells are attached very quickly and some compressed air to cool it down quickly.
Lots of videos on repacking computer batteries worth watching.
If you just have one or two bad cells then replacing them will be fine.
However these cells are prone to exploding and this gets worse with age so many have a counter in the control circuit built into the battery and these can not be reset.
After "x" number of discharges they shut down and that is that.
Attempting to bypass the control chip usually ends up with the cells exploding or the house burning down.

There are some specialists battery remanufacturers but weather they do your particular battery will depend upon demand as it is labour intensive.
The other problem is getting the exact same cells to replace the bad ones.

I have done a dozen or so for my old Wallstreet laptop with about 60% success because you used t be able to get the replacement chips.

 

[ilyaz]

I watched a couple of Youtube videos about people converting cordless mowers into corded. Might want to try it just as a fun experiment (hopefully not resulting in electric shock, fire or explosions )

So I am wondering if I can wire in something like this. It says 40V output but only 0.5A, so not sure if that would be enough for the mower to actually cut grass.

 

[1 Lucky Texan]

I watched a couple of Youtube videos about people converting cordless mowers into corded. Might want to try it just as a fun experiment (hopefully not resulting in electric shock, fire or explosions )

So I am wondering if I can wire in something like this. It says 40V output but only 0.5A, so not sure if that would be enough for the mower to actually cut grass.

10 of those in parallel wouldn't be enough.

if you can use corded, just buy one. small-ish yards with few obstacles are good candidates. I used to like to start near the house and work 'outwards', leaving the cord on the new-mown surface. I always preferred the 'reversible' mowers with the swing-over handles - dunno if that style is made anymore but, much less cord flipping/whipping/manipulation.

 

[ilyaz]

10 of those in parallel wouldn't be enough.

Ok thx that's good to know

Hate to throw out this working mower but it might be the only viable option at this point

Although just now I found this posting on eBay. Model numbers are different and the price is much lower than anything else I've seen so not sure if this is legit and would match my mower. Sent a message to the seller but no response yet.