Can you revive NiMH batteries?

[burakol 462]

22 minutes ago, No Slack said:

My second HPI Plazma accepted a charge of 4000 mAh but is also a bit weak speedwise. But it seems both batteries come to life a little. Next cycle is now happening.

I'm also cycling 2 of the five packs I currently have... what charger are you using, and what voltage are you discharging yours and at what discharge and charge rate?

I'm doing mine at 1amp for both charge/discharge  so for a 5000mah capacity battery, im anticipating it to take the whole day...doing 2 cycles today... doing it both on my clone Imax B6. 

[GregM 1109]

5 hours ago, burakol said:

Whoa! 

Out of curiousity, anyone here tried to re-pack their NiMH? I am currently debating if I should open mine up and see which cell is kaput and try to salvage the usable ones...

I tried and made quite an accidental mess of battery fluids leaking into the fireproof container I used for storing them. Blergh, that fishy smell.

[No Slack 454]

10 hours ago, burakol said:

I'm also cycling 2 of the five packs I currently have... what charger are you using, and what voltage are you discharging yours and at what discharge and charge rate?

I'm doing mine at 1amp for both charge/discharge  so for a 5000mah capacity battery, im anticipating it to take the whole day...doing 2 cycles today... doing it both on my clone Imax B6. 

The settings I tried are: discharge under constant voltage with 35A using the Spintec-discharger and, after a very long cooling period, charge with 3.5A. The charge setting of 3.5A  warms the battery but but my Imax B6AC V2 cuts off in time.

The NiMh's take a charge now and you can use them for bashing but are not good enough for top speed. Maybe after a few cycles the batteries will again be a little better. I will let you know.

[•Axle 145]

After almost 30 years of not going near a decent RC car I bought 3 NiMH 4000aAh and a new charger that also did lipo just in case I wanted to change in the future. You know 3 batteries, that should last me and my daughter and few runs up and down the park… I’m literally spending most of the day trying discharge the batteries, they last so long!

I remember discharging batteries with a wired up lightbulb!

[MadInventor 3884]

16 hours ago, burakol said:

Whoa! 

Out of curiousity, anyone here tried to re-pack their NiMH? I am currently debating if I should open mine up and see which cell is kaput and try to salvage the usable ones... 

I certain that there's some good cells in my packs as it still packs a punch but just doesn't last long anymore... 

Yes, I've done this on several occasions. I used to  build my own 9.6V NimH packs , and not having used them for a few years, tried the discharge - recharge trick to find one or more cells had died, so chopped the packs and rebuilt them with all good cells. I've also done it with prebuilt packs, where I had dead cells in one pack, so cut it in half and added the good cells to  another pack to make a 10.8V 'triangle' pack to fit in a TT-01 for doing speed runs. I've also had good success with reviving Ni-mH packs that have been dormant for more than 4 years, and got them back to 90%+ of their original capacity.

[rich_f 233]

As the previous poster mentions, opening up a 'dead' pack often reveals that only one or 2 cells are actually bad and you can use the rest to make up a good pack with other cells. I recently brought a cordless drill battery back to life by swapping some of its (Nicad) cells with some from a 'dead' rc car stick pack, which uses the same size cells. 

Regarding reviving old packs in general, I was out of the hobby for over 10 years and I've only ever had success reviving packs with low nominal capacity. All of my 3000+mAh packs had dead cells and even when I repaired them with good cells from other packs, they soon died again. 

My Nicads 1500s and 1700s are good as new, despite being over 20 years old. 

I imagine that the short life expectancy of high capacity packs is due to the manufacturers cramming more stuff into the same size cell, meaning that they are less resilient to the ravages of being used, i.e., they far more easily develop internal shorts.

[burakol 462]

9 hours ago, No Slack said:

The settings I tried are: discharge under constant voltage with 35A using the Spintec-discharger and, after a very long cooling period, charge with 3.5A. The charge setting of 3.5A  warms the battery but but my Imax B6AC V2 cuts off in time.

Are you using an original B6 charger? 

I tried one of the pack I cycled yesterday...initially, my rc was cutting off at full throttle literally during the first 5 minutes.. then I was running it half throttle first then pulling the trigger all the way... it seemed to work and for whatever reason, it looks like it "awaken" itself and held a good amount of charge...after 15 minutes of just running my GF01 around, I called it a day... theres still left in the pack and I'll try to run the same battery when I get home later... 

A lot of work to revive it... and I've only tested 1 out of the 5... 

[Grumpy pants 4485]

Well it has taken me months to recharge the remaining 2 batteries to try and stimulate them into action.

Sadly battery 2 is as dead as a dead thing and the 3rd battery hold some charge and works but nowhere as well as it did.

I’ve had them 7 years or so and used them intermittently but next time I’ll take better care so that I can extend their life expectancy.

[xray mark 213]

you need to break up the crystals that accumulate inside

flash the batteries across the terminals of a 12v car battery For a second This will jump start them back to life. 

[catman79 346]

once an nimh pack dies, its best to give up on it, generally they cant be revived to a useable standard, and at the cost of new ones isn't much, its not worth messing about. 

my advice to anyone these days would be to go to lipo, they are like night and day, and once you've gone lipo you'll never look back!

[Mad Zero 316]

On 9/2/2020 at 4:27 PM, xray mark said:

you need to break up the crystals that accumulate inside

flash the batteries across the terminals of a 12v car battery For a second This will jump start them back to life. 

Yes dendrite formation shorts the cells but it can be dissolved with a short sharp shock. Capacitors are best for this because they give you a high voltage for a very short time. Common way to do it was with a 4700uF 35v ish cap charged from a 12v car battery (but more volts, say 20 or 25v would be even better if u have a suitable PSU) then just flash the terminals of the pack to break the short. Hey presto a working stick pack… most of the time.  

[DPR250R 55]

I bought some old but new packs to break them apart and reconfigure. 
 

They were so dead my smart charger would not recognize them. I ended up buying a radio shack slow charger and and letting them sit on it for an hour or so. Went back over to the smart charger… good to go! 

[El Gecko 1344]

I've successfully revived a decade-old NiMH and am still using it. It has good capacity (runtime) but lacks the power/punch of my newer packs. Perfect for fragile old cars with MSCs

[Dakratfink 967]

On 5/27/2020 at 3:26 AM, •Axle said:

After almost 30 years of not going near a decent RC car I bought 3 NiMH 4000aAh and a new charger that also did lipo just in case I wanted to change in the future. You know 3 batteries, that should last me and my daughter and few runs up and down the park… I’m literally spending most of the day trying discharge the batteries, they last so long!

I remember discharging batteries with a wired up lightbulb!

This was EXACTLY my experience a few years back when I got back into the hobby.

I was blown away by the performance I got outbid a Nihm pack with car cigarette lighter charger. It was miles ahead of my old NiCds I had as child. 
then I eventually upgraded to Lipo is was like Aladdin “A whole new World”

[Nikko85 3454]

I really wish that batteries like this came in a sleek holder, so you could pick and choose cells.

It would be so much better for the environment too. Throwing away a pack as one cell is bad is just a bit crap really, but not much else you can do.

One tip I have found,

For some NiMH AA batteries that can't take a charge if you put a 9v battery on them for a quick sharp shock (careful, don't do it for too long) it can shock them into working again. It's usually on packs that have been left on overnight and the battery is 100% gone.