OT Replacing the batteries in a cordless drill battery pack

I've got a couple of good, relatively light weight 12v cordless drills (about 6 or 7 years old). The battery pack capacity is just not what it
was years ago. I know there is an outfit that rebuilds the battery packs with a greater current? capacity Ni-cad. I just don't want to spend quite as much as they want for a single battery pack rebuild and I don't mind spending a little time to do it myself. I was in Sears a few days ago and bought an 18v battery pack - new, open box, customer return for $23 in the bargain area in the tool department. I intend to use this as a source for the batteries needed to replace the ones in mine.
The batteries in my old pack are labeled: N-1300SC. THe ones in the Sears 18v pack are labeled: N-1900SCR. I assume the N is for Ni-cad. Does the 1900 imply a higher battery capacity, what are the units? If so, could the extra 1900 battery capacity overtax the old 12v charger that was intended for the 1300 batteries? I'll have 5 c-size Ni-cads batteries left over - can I buy 5 additional batteries and upgrade another battery pack - I assume that I will need Ni-cads that are rated at 1900? THe leads between the batteries are metal strips that appear to be resistance welded between the batteries. I assume that I can solder wires onto the ends of the batteries - correct? Is there a way to test each Ni-cad in a pack - I have one old battery pack that shorts out the fuse in my charger if I plug it in? Thanks for reading this far and I'm hopeful for answers, directions to links or suggestions.
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Take it to one of those places that deals in batteries, I took a sears one for a friend and they put in a new rechargable one
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I ran onto this site while searching
http://nicdlady.com /
--

- Charles
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-does not play well with others
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There's also info on rechargeable batteries and how to assemble packs at http://www.rcbatteryclinic.com if that doesn't work, google reds battery clinic. Pat
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1-800-DIGIKEY
For little more than the cost of new cells, you get a rebuilt pack.
To read about my senior project at ODU, Go to Google Groups and enter dgoncz along with any or some of these words: ultracapacitor electric bicycle motor generator fluorescent energy display
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aribert wrote:
<snip>
You sound almost as anal compulsive as me when it comes to keeping old stuff running just for the sheer joy of proving you can do it, even if it means my time is worth less than a buck an hour while I'm doing it. (One of the many blessings of being semi-retired.)
Less than two weeks ago I replaced the four Sub-C nicads in our kitchen B&D dustbuster for the second time in it's 18 year life! I sprang about $18 for those four cells (the kind with solderable tabs welded on) at Radio Shack just because it was more convenient to pop in there than to find and order them from a web store and wait...
I also replaced to pair of C-sized nicads in my bird feeder which were about three years old and are trickle charged by a little solar panel I added to the feeder. (Never seen an electric bird feeder? Go to:)
http://www.yankeeflipper.com/droll/index.cfm

The units are milliamp-hours. Anyway, you are correct that the larger number indicates more capacity, and that shouldn't bother your charger one bit, it'll just take a little longer for them to charge.

Yes on the 1900, and you should be able to do that transplant *if* the batteries from that old "returned" pack weren't returned as "unused" after someone had really had the pack for several months and cycled them lots of times.

It ain't easy to solder directly to the batteries without damaging them from the heat. That's because they have such high thermal conductivity that you get their guts pretty hot by the time you get the part you're trying to solder to hot enough to wet with solder. That's why the tabs are spot welded, with one quick pulse of heat right where it's needed for fusing the two tiny welds. They ain't like the old "LeClanche" dry cells with zinc cases and a brass cap on the central carbon rod. Those were routinely soft soldered to by both battery manufacturers and hacks like me.
Those tabs should be easy to soft solder to, because they're thin, and the right material. That's why I sprang the few extra bucks at Rat Shack when replacing the Dustbuster batteries. Just cut 'em in the right places to leave a bit to solder to.
You can also use conductive epoxy to connect wires to Nicads. That stuff is a bit pricey, but a little goes a long way. And, if you keep the unused stuff in the freezer, it'll still be good years later.

Generally, by the time one or two Nicad cells in a pack short out, the others aren't worth using save for emergencies. And, it isn't good practice to mix new cells with old, it can get you into the wonderful world of "reverse charging" the older cells during discharge, which sure don't help their remaining capacity one bit.
But, assuming you've got multimeter with a voltage scale on it (HF is now selling their cheepos for less than $5!) you can "test'" them by charging up the cells one by one and see whether the voltage across them starts rising and comes up to about 1.3 volts after a few minutes of about 100 ma of charging current flowing through them.
You can get close enough to 100 milliamps just by picking up a 100 ohm 5 watt wirewound resistor at Rat Shack or elsewhere and putting it and the cell in series across either your charger's output terminals or even a 12 volt car or motorcycle battery. If the cell you're trying to charge has an internal short, the voltage will not rise above zero much if any. Watch the polarity, and make sure that if you use a charger it has internal isolation and doesn't end up with line voltage on either of it's terminals. (Wedging in a disclaimer.)
Measuring old cell's storage capacity is quite a bit trickier, and is left as an excercise for the student.

Jeff
-- Jeff Wisnia (W1BSV + Brass Rat '57 EE)
"If you can keep smiling when things go wrong, you've thought of someone to place the blame on."
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Thanks for the replys and links. I'm glad I asked first before tearing off the metal tabs and trying to solder jumpers to the battery ends! Looking at the prices for the exact same sub C Sanyo battery as used in the 18v Sears unit at the Nicad Lady website, my $23 for the 15 batteries out of the sears battery pack is quite a bit better than $4+ each from the the online store.
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As a last resort you can gut the battery pack compartment and put in a minijack and feed the power externally.You give up compactness but gain the advantage of having a limit decided by your battery pack.You may find this out when the internal batteries cost more than the whole tool when purchased.Have done this many times on power drills.
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