So let me get this straight.

You had an OLDER 18 volt battery that no longer wanted to accept a charge from your charger.

So you connected a GOOD 18 volt battery that was fully charged and connected it to the older battery directly by hooking negative to negative and positive to positive and then sat back for 10 minutes or so while these two batteries talked to one another. Do I have this right?

And after doing this, the OLDER battery will now take on a charge once more. OK- got it.

So, let me ask you this.... After the charger tells you that the OLDER battery is fully charged, now much run-time do you get out of it compared to what a new battery would give you?

I'm pretty interested in this because I've got DeWalt and Milwaukee cordless tools worth hundreds sitting around doing nothing thanks to Ni-Cads that no longer work.

Kompressor; What needed on these batteries bring back up orginal voltage every time charge they loose some there volts 18 volt battery going to be weak at 14 volts this happen even if battery just out charger called loosing battery memory. 2 Tools you need to get back to orginal volts multimeter and battery larger that volt trying to bring up and mini jumper cables for batteries. On battery you trying to repair volts on touch larger volt battery just 3 to 5 seconds recheck volts remember you want bring up to 18 volts then stick in charger for charge. I f you can't get battery back to 18 volts there cell bad in battery will need replacing. If never get a old battery to go above 0 then strap from battery to battery is broke inside pack moisture on strap rust in short time. There a lot more to bring back all types batterys but wear safety Glasses on what working very important. you use any battery combos to get above 18 volt its volts that important.

This Ni-cd battery resurrection thing has come up several times. There are even instructions you can buy that tells you how. Been there done that. Does it work? Yes.....to a certain point. Is it worth it? No. Batteries that are shot are shot. This method allows a certain small recharge capacity but it doesn't last. The batteries do not have there full capacity. I did this with several battery packs. All were dead not long after. Try it if you like. Nothing ventured nothing gained. If you're planning to build a deck with your resurrected battery forget it.

rdaystrom,
That's pretty much what I thought which is why I asked the OP about battery CHARGE longevity. It's one thing for a battery to READ 18 volts and something else again to PUT OUT 18 volts for an extended time. Thanks for your reply.

Batteries last 3-5 years. If yours lasted more than that then consider yourself lucky. If you have a way to take something that is dead and bring it back to life, you can probably make a alot of money selling that idea. Meanwhile, on planet earth, even a dead battery can show some signs of life, but its still on its death bed. Even though you brought the battery to the point where that charger 'sees' it, you will not be able to do real work with it. Try driving 4 inch deck screws and seem how far you get. I doubt you can drive a single one. Measureing a battery with volt meter is only a very basic test. Measuring it under load is a more real world test. Its unfortunate that with these Korean cordless drills, that the battery cost more than a new drill (with a new battery). If your drill cost $300 then you would see how attractive it would be to spend $50 on a new battery.

I have drills that came in kits by DeWalt that cost me $350.00 but here in Canada, I can't buy a battery for $50.00. The same with the Milwaukee kit that came with a flashlight, SawzAll and drill.

I'm semi-retired now so I don't necessarily use cordless tools every single day. Ryobi isn't what I call "Pro level" tools but for my purposes, they get the job done. I can buy two new 18 volt batteries for around $60.00. Works for me. And I certainly know the difference in quality between the Makita, Milwaukee and DeWalt tools I used to use and the Ryobi stuff I use today.

ditto, on kompressors thoughts of the good stuff. I too had dewalt (batteries was 89 apiece when I got rid of mine) and soon learned the real money was in the batteries. I dumped them and got me the cheaper Ryobi knock offs "Craftsman". I got more play tools drill, light, saw, recep saw, right angle drill and ????? so many I can't think of them all!!!)and the batteries are 1/3 to 1/4th the price. I too use them around the house and they work just fine for my dinky jobs. 19.2 volt batt. last me about 1 ro 2 years. But I buy the two pack for under 50 bucks usually.

Are you tired of having your Ni-Cad batteries that refused to charge and simply die?

So what do you do with them when they die?
Just throw them in the trash - which harms the environment?
Or just take them to a recycling facility for them to be recycled?

Well, here is the best solution, bring your dead batteries back to life that can save you a chunk of change - By zapping them!
Here is one great instructable, Revive Nicad Batteries by Zapping with a Welder. Of course, you will need a welder, and not many people has one... So I came up with this idea that almost anyone can build!

Here is a link that might be useful: Drill Battery

This jerkwad is just shilling some questionable website.