NiMh Batteries life limits

[OMGWTF]

Ok just a quick question

I have two 9.6v NiMh batteries one @ 5000mAh and another @ 3200mAh
I have not used or recharged these in over 4 years.. they have been stored in a cool dark place the entire time.. Normally if they were NiCd batteries I would just deep cycle the battery and carry on hoping that the memory it formed isn't too low.. However with a NiMh I dont think you can deep cycle like you would a NiCd.. I know they are less prone to forming a memory but I think 4 years of no use and not being charged before storage might cause an issue.. Anyone have experience with batteries being stored for that duration and then suddenly being put back into service?

I'm curious if there is a reconditioning procedure I could perform or if I should just invest in some new batteries.. we all like saving a buck right?

[SuperHog]

Depending on the charger you have, you can cycle charge them. As long as the cells are not leaking, they should be fine.

[8bitninja]

They'll be fine after a few cycles. If you want, I can condition and run them through my CBA III to tell you what the current capacity and discharge curve is.

[ThunderCactus]

NiMH batteries lose 9-12% of their charge per month. So your batteries are right the fuck DEAD. 0v.
However, the issue is not charging them back into life, as you can absolutely charge any nickel chem battery back up to full form 0v. The issue is at 0v, the individual Ni chem batteries can actually REVERSE their polarity.
SO, try charging them and see what happens. But since Ni chem batteries heat up while charging, I'd advise you to charge them for half an hour, let them cool off, then charge them another half hour, if they're not full then let them cool down again.
A full charge from nothing should technically take 1 full hour, but they can get pretty darn hot charging at just 1C.
But if the pack's dead, it's dead. In order to fully revive it, you'd have to de-solder each battery and charge it into the proper polarity individually.

[Hectic]

Seems like a lot of work when decent lipos for most setups (especially one running nicads) are 10 bucks these days. Check out hobbyking there lipos are decent considering the price. Buy 3 or 4 batteries shipped for under 50 bucks. Won't need a charger for a while, but a decent lipo balance charger isn't all that expensive either.

[8bitninja]

Originally Posted by Hectic

Seems like a lot of work when decent lipos for most setups (especially one running nicads) are 10 bucks these days. Check out hobbyking there lipos are decent considering the price. Buy 3 or 4 batteries shipped for under 50 bucks. Won't need a charger for a while, but a decent lipo balance charger isn't all that expensive either.

That's a good point, depends what you're using them for. I pulse charged and reconditioned my dead for two years Roomba NiMH pack (each cell) back to health. Since its at work anyway it saved me $50 on a replacement and has about 80% usable capacity before heavy voltage drop. So if it's a unique battery, recondition it (if you have the means or send it my way). Else if it's just a normal stick or hump pack, get another... Save yourself the time

[ThunderCactus]

When NiMH batts die, I just replace with lipo lol
Ever run a dust-buster on an 11.1 lipo?
MOAR POWER! MOAR ENERGY! MOAR VACUUMING!

[Styrak]

I had some Intellect 8.4v sticks that I sorta brought back to life after sitting for 2 years. Charging them on 1A or 1.5A didn't work, only put about 200mAh into them and said they were full. Dropped it down to a 0.5A charge rate and it put a full 1200-1400mah or so charge into them.

[8bitninja]

Originally Posted by Styrak

I had some Intellect 8.4v sticks that I sorta brought back to life after sitting for 2 years. Charging them on 1A or 1.5A didn't work, only put about 200mAh into them and said they were full. Dropped it down to a 0.5A charge rate and it put a full 1200-1400mah or so charge into them.

If you can discharge each cell down to 1v at 0.1c you'll be on your way to reform the battery. A effective recondition takes about 16 hours. Unless it's a special form factor, might as well buy new if you don't have the time or patience

[8bitninja]

Here's an example for you. This was a relatively dead 7-cell NiMH with marked capacity of 1100mAh. Charged up, it barely ran so I did a cycle test and the first 2-3 cycles netted between 100-300mAh (0.5a discharge rate to 1v per cell). I ran another 5 cycles with my parameters and the capacity increased to 400mAh. Seeing a little bit of progress and an ok cell resistance value, I cycled the complete pack. Below are the current results which are promising. I'll test the individual cell resistance on load again after the set of 10 cycles to see if we have a usable pack. I consider it a success if the resistance values are acceptable and the overall pack capacity for 0.5a discharge at 800mAh. If it reaches 900mAh, I'd consider it similar to the rated capacity of 1100mAh if they used the IEC testing standard (ha!).