raising 18650 back from the dead, samsung 25r

[ridethelightning]

Hi guys.
iv got a relatively new 20s10p 25r pack that was neglected by a friend and given to me, and has probably drained flat very slowly from adaptto controller being left connected.
total pack charge is like 2.0v

has anyone had any first hand experience with this particular cell or chemistry's behaviour when flattened completely like this?

hoping to try to revive them slowly, but would like to avoid a fire

any advice appreciated.

RTL

 

[Hillhater]

Open it up and charge the 10p groups individually ( low charge rate)
Check groups for voltage retention, and capacity, etc.
Any weak or odd group performance ...split out to individual cells for more checks.
That way you can see which , if any, cells are dead.

 

[ridethelightning]

thanks for the pointers.

was planning ~0.1A /10p group to start off with,using hyperion, so i guess around 0.01A/individual cell.

any idea if cells like this can cause fire, even after they have taken and hold full charge well?
just dont want an incident some time down the track..

 

[Syonyk]

2.0V across a 20S pack is roughly 0.1V/cell - but if you measure, I bet you'll find at least one group that's been driven negative. I've received a lot of dead or nearly dead packs, and they're never consistent across cell banks.

And, that said, I'm not aware of any safe way to use a normal lithium battery from that voltage. Lithium titanate can be repeatedly drained to 0V and charged, but nothing else can.

I have deal with plenty of used packs, and I have a standing policy of not trying to charge anything that's below 2.0V/cell - and I'd want to know why it's at 2.0V before charging it. Below that, in my opinion, it's simply not worth the risk of charging a certainly-damaged cell. Maybe you'll be lucky and it'll work. Maybe you'll be lucky and it will get hot as hell and melt its wrapper on the first charge. Or maybe you won't, it'll hold some charge, and fail catastrophically when mostly charged in half a dozen cycles. There's simply no way to tell what it will do.

I might use something like that if I were using it as a stationary storage battery, outside, in a fireproof concrete enclosure I'd designed to contain batteries. Maybe. That's the only thing I'd consider with something that has the potential to go up in smoke and flames. Two hundred 18650s, 2500mAh each, is around 2kWh of energy, and a cell burning its electrolyte will usually emit twice its rated energy (so you've got about 4kWh of potential thermal energy you're looking at containing). That, going up in 5 minutes, is a sustained heat flux of around 50kW. Do you really want to mess with that?

Check the cell group voltages for any negative voltages before you follow any of the advice you're sure to receive from other people.

 

[Adverse Effects]

i have to agree with Syonyk 100%

 

[skeetab5780]

Odds are even if you single charge each parallel string and they hold voltage. They will heat, have loss of capacity and also lose charge while resting and deplete back to nothing without repeated use. But if you cycle them daily and only need 8ah out of a 20ah pack then you may be able to revive them sort of.

Just obviously use precautions while charging since you never know what can happen. Even though 18650's are sought to be fairly safe, I've seen simple solder errors turn things red hot and dangerous.

 

[ridethelightning]

thanks for all the info guys. even though some is hard to swallow, it may just save bike/house form burning down..

 

[Syonyk]

Just obviously use precautions while charging since you never know what can happen. Even though 18650's are sought to be fairly safe, I've seen simple solder errors turn things red hot and dangerous.

Charging, riding, and while sitting.

Lithium chemistries are physically damaged by being fully discharged. That damage may manifest as reduced capacity/increased IR, or may manifest as a cell failing via thermal runaway, which leads to aggressive venting of flammable gasses, often sparks (hey, now you've got a blowtorch!), and the evolution of incredible amounts of heat in a short period of time, which may cause neighboring cells to enter thermal runaway.

To be safe with damaged cells like that, you have to treat the pack as though it will burst into flame at any point.

That's, to me, not worth the risk. Even for free batteries. I've got a stack of dead LiMn cells that I have no interest in playing with because they've been deeply discharged.