traction battery and extra long term storage

I know this has been covered before but a long time ago and no real definite answer in any previous threads.

extended periods of hv battery storage (years) ...

If traction battery sits in storage unused for multiple years will the modules self discharge past a point of return? I understand they can sit almost indefinitely "if stored above 7.2v" I understand the pack needs to be re-charged before its put back to use, at some stage (months/years) even good modules must self-discharge under 7.2v and eventually reverse?

So battery gurus, has anyone let a hv battery pack sit in storage for multiple years and if so what happened did it survive?

Matt

 

hi thanks for your reply, yes I have a grid charger but some are saying these NIMH batteries are best stored almost completely discharged others argue that, I don't want to go back to a pack in 2 years and every module is shot because I did not store it properly.

yes that's one way they can reverse but I believe they can also start to reverse if they self discharge too much

would love to hear from anyone that has stored batteries for a few years

 

thanks fotomoto never noticed this thread before, reading now..

 

Thanks tpenny67 will try to quit worrying about it, was just looking for re-assurance that its definitely safe to let spare packs sit dormant almost indefinitely as a few ppl on here have suggested, I do understand that I need to charge them before loading them in any way I just cant get it out of my head that simply letting them sit discharged (for years) will be their death sentance.

Very interesting thread about the guy with the brand new 05 but so far he has not said if that battery was still good or not, either way if that pack ends up being bad its hard to say if long term storage killed it or being so discharged at the time of spinning the ice for the first time in ten years could well have pulled a cell backwards I guess we will never know

 

naah 40% after 10 years is not really possible even the best module will self discharge a few percent per week after 10 years it seems very unrealistic that it could be anywhere near 40% soc, I would think it was under 10% and thats at best more like just chemical base voltage of 7.2v but effectively 0% soc but the car didn't have a chance to log a code before the battery started to recover once the ice got going, the guy did mention warning lights and red car displayed on the MFD on his very first drive.

 

I think from what I understand even a "flat" or effectively 0% SOC module will have a couple hundred milliamps sitting at base voltage (7.2v being the lower limit of a "flat" module due to its chemical makeup) that couple hundred mA would be almost enough at 201.6v to spin up the ice just once but it would yank on the modules very hard in doing so, the car monitors for a short time before reporting a code and in that short time the battery has a chance to recover enough to keep the code away. Car can charge at very aggressive rates when it wants to.

that's my take anyway I could well be wrong, NIMH cells suffer from dramatic amounts of self discharge so I don't understand how after 10 years it could possibly have anywhere near 40% soc ..if I leave a charged module sitting for 4 or 6 months it starts to head down the hill towards 7.2 very rapidly.

 

hi Dolj thanks for replies yes I understand discharge is not linear however something still just does not quite ad up when it comes to that car, as you would know 215v is around 7.7 per module, if I leave a 100% soc module on my bench its usually down near 7.4min /7.6max by the next time I look at it.. and that's after a few months not ten years!

So the question is ..what happens once hibernating modules fall below chemical base voltage, or wont they..

We shouldn't keep using that particular 2005 car as an example anyway being such a rare situation

 

Thanks Jeff its reassuring hearing this from yet another with such extensive experience, Steve has also tried to assure me on more than one occasion that its fine to let them sit I'm a bit of a worry wart! I don't want to waste my spares by simply letting them hibernate a couple years.

Only thing makes me think twice is the example cars both being barn finds would have exceptionally good modules, as new even..hopefully the theory is not different for matured modules.

 

hi all, just wanted to touch on this subject again!

I recently picked up a 2004 pack that was really flat every module in the pack was under 7v.. must have been sitting for a very long time. Grid charged it at 350mA to 242.48v then a 24 hour rest prior to discharging at 18A ...4 modules tested 5000mA the rest of the pack was around 1000 or less. Cycled the modules 3 times but nothing changed

Also, this time last year I tested some modules and noted their capacity most were around 5000mA after 24 hour rest so I charged them to 80% for storage, I cycled and retested those modules again this week and most are now 4300-4500 ..

something is happening to batteries in storage, anyone else having this issue ?

Matt