I've been told that you can "blast" your battery to recover a bad cell. How do you do it?

Yeah, you can blast a battery and yourself and your house along with it if you don't know what you are doing.
There are ways to bring up a bad cell, never heard of "blasting".

First of all, what kind of battery? Second, how do you know it has a bad cell? I.E. what voltage reading on that cell?

If you suspect you have a bad cell in your battery, even if you think you have recovered it, it's best to leave that one on the ground and not fly a model airplane with it. If it gives out in the air, well, you will lose more than a battery.

CGr.

Totally agree - I file bad cells in file # 13 (bin). No way would I take a chance on any bad cell for anything that goes in the air. You might play with it on some surface stuff, however that is as far as I would go. Really when you think about it, the cost of a battery is not worth the effort unless it is something unusual and high dollar then it may be worth a shot.

I have "pulsed" 14v NiCd packs for power tools using a welder and it works for me.  Some packs are still working years after.
 If the flightpack cell has very high resistance or has vented it won't help it.  I have spent time trying to salvage NiCd packs,making one out of two, etc... and decided it's not worth the time and now replace failing packs with LiFe flight packs.
If you are referring to a LiPo cell , just disable it and toss it.

I agree, the cost of a new battery just makes screwing around with a bad pack a no brainer. It also is not worth the risk of getting hurt or having a fire. Just make sure you dispose of the old battery correctly and move on. Good luck, Dave

It is done only on NiCad cells where one cell in a pack is not showing voltage and won't take any charge. It is done by touching a 12v source + to + and - to - , too the cell momentarily like in 1/2 second. Often it will revive the cell but sometimes only temporarilly but if the pack is then left on a float charger, the cell is generally trustworthy as long as the pack meets the 70-80% capacity test.

Like I said... this might work for something to use on the ground for anything other than actual flying. There is to much at risk to use something that questionable during actual flight.

CGr.

Are you saying you wouldn't risk one of your high dollar planes by using a pack that may fail??? Something that can be completely replaced for just a few dollars?? Rather narrow thinking when you can just blast that bad pack and go fly.

I've shocked nicads back to life before, but only in cordless phones and stuff. I wouldn't trust it for use in a plane. Dennis

Well....... yeah.

I've told this story before, but here goes. My pattern plane, Venus II with an OS 1.20AX has a dual battery pack setup... both 5 cell NiMh packs. They are connected in parallel, each has it's own switch. I use a voltwatch2 on the plane to monitor battery condition and check it before and after each flight.

I was flying one day, I seem to reecall it was after the third flight or so, and after landing, I checked the packs, individually, as I usually do. Pack 1 checked out OK but pack 2 showed down in the red zone without moving any of the sticks. Battery pack 2 went bad during the flight.

Had I had only that one battery pack, well, my Venus II would be a pile of balsa and light ply.

The point here is that they can and do fail in flight. Adding the situation where the pack was "shocked" and probably temporarilly restored, well, that's just not worth it to me. Add the situation that if it happens where there may be several people there, and it fails as the plane is headed in the direction of the crowd.. well, I'm sure you get the picture.

CGr.

I second flying it in file 13.

The best possible use for Questionable flight or Tx batterys is something like this simple servo driver/exerciser or even just a spare battery pack kept charged and convienent to the work bench for powering up an aircraft while working on it:

Never in a airplane you actually intend to fly.

John

http://www.youtube.com/user/JohnBuckner100

You can sometimes get a Nixx battery to work by putting a high current pulse through it for a few milliseconds. The reason this works is that, as a Nixx cell ages, thin breaks occur in the membrane separating the two plates and crystals form a bridged short between them. The high current pulse burns out (vaporizes) that short and removes it. However, the hole is still there in the separator and new crystals will soon form and short the cell again. And, while the cell will appear normal and chargeable, it will never be a reliable energy source again and can fail at any moment so use only where such occurrence will not become a problem.

I have two dead packs on my bench, a 4.8 and a 6 volt. Both have the ends cut off. They are there so I can use them when building a plane and I have a pack to check and set the CG. The other use is so I can see how they are both wired in case I want to make up my own packs. I do make my own but I have a different way to do them that doesn't involve soldering but just in case I feel like giving the soldering another try I have the packs to make sure I don't make an error in the way they are wired. I think the cheapest plane I have is one I built from scrap wood from a set of plans someone gave me. The engine was only $100.00 and I used cheaper servos in it. Using parts I had on hand it is a free plane with maybe $200.00 worth of parts. That is pretty cheap but I'm still not going to risk a $200.00 plane over a $20.00 battery. My other planes are more in the thousand dollar range with high dollar engines and servos. Why anyone would bother trying to fix a battery pack is beyond me. I have an Eneloope pack in the shop now with a dead cell. Those are high end batteries but when it is there time to die then it's time to file them away in bin #13 and move on. RIP!

Yup...

Questionable NiCD / NiMH packs can be disassembled and the individual cells ( once tested ) are great for glow ignitors, bench testing, and even for electric starters...

But for RX/servo electronics? No way.