On Tue, 28 Jun 2005 20:33:51 -0500, "Paul Gilbert"
wrote:

My Dewalt 18v batteries have slowly been headed south. One is shorted and
two others last about 5 min. in a drill. Batteries Plus wants $50 to
rebuild the battery and new ones cost about $65.

Today I went to Harbor Freight and purchased a 18v battery ($14.99) for
their drill and then went home opened up the DeWalt and Harbor Freight
battery packs. They have the same individual cells (15 x 1.2v), but the
individual cells are spot welded together with a strap which keeps them in a
fixed position. I can't force the Harbor Freight batteries into the format
of the DeWalt pack.

The last time I tried to solder batteries together it didn't work. Anyone
know how to cut the straps and solder the batteries back together?

I've bought brand new Dewalt 18V batteries for $50 a piece at the
local ACE hardware. They come in a 2 pack for $100. Now I have to
admit, it is an unusally well stocked store with power tools of all
kinds but I've even seen the 2 pack at Home Depot for $120.

You have to be careful with the HF batteries. In all likelyhood
they're only 1 AH cells while the Dewalt cells are 2 AH so you'll get
about twice the run time on the Dewalt pack.

Soldering is no big deal. I do it all the time. I usually dont cut
the flat strips but grab them with a long nose pliers and pull them
off the button (+) end of the cell, never the bottom (-) end if I can
help it. The button is just a tiny piece of metal and heats up
quickly without damaging the cell. Ulling the flat wires off just
breaks the welds holding them to the cell but usually leaves the wire
intact and long enough to reuse.

You need a high wattage soldering iron and some sandpaper. The cells
seem to have a coating on them that doesnt take solder too well and
requires a lot of heat to burn through. you can avoid all that by
using the sandpaper or a dremel tool to scuff up the bottom of the
cell or the button first. Then its just a quick light touch with the
high power iron to tin the cell (thats the secret, pre-tinning).

Since the flat wire was ripped off instead of cut, its still long
enough to be soldered back onto the button of another cell. If not
already flat, flatten it in the jaws of the pliers, scuff the wire,
and tin both the cell and the underside of the flat wire, then, using
a screwdriver, hold the flat wire onto the cell, tinned cell to tinned
wire, and just use a minor amount of heat to melt the tinning. Bingo,
the cells are soldered together.

As someone else said, too much heat damages the cells.
So three secrets:
1, scuff the metal before tinning
2. tin both surfaces quickly
3. heat quickly

dickm