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?
Been tempted to try a similar approach on a bad 14.4 volt battery I have. I
watched a local outfit repack a battery for me and they used a small spot
welder to attach the straps to the individual cells. Perhaps with the
correct solder and flux the straps could be soldered but I think this is a
case where having the right tool (spot welder) is the trick to a successful
You can solder wires onto the straps but if you try to solder directly
to the batteries you will dump too much heat and ruin them. You need a
spot welder to attach straps to batteries.
(remove all letters after y in the alphabet)
You can freeze the cells and use a soldering gun- I use a 140 watt gun and
do it easily. BTW - I hope you have better luck with the harbor freight
cells than I did. They had an unreal self discharge rate. Lost about 50% of
their charge in one day! I ended up buying some out of date battery packs
and soldering replacement pack to keep the old 9.6 makita stick batteries
and a old black and decker 9.6 alive. Not to mention that if you use ther
harbor freight cells, you might fry them in the standard charger for the
dewalt batteries. There are certain types of nicads that are meant for high
charge rates. Not saying it won't work- just that it might be an interesting
Or you can do what I did:
Buy a new Milwaukee drill on sale for $175.
Resell the 3rd battery that comes with it (through a mail in rebate) on ebay
Resell the original Dewalt Drill with nearly dead batteries on ebay for
So for $25 I was able to upgrade to a better drill with brand new batteries.
Not too bad.
Joe in Denver
my woodworking website:
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
Good advice, cleaning, tinning, a high power iron and being as quick as
possible is the key. I would, however, tend to stay away from the + end
since there is a plastic vent underneath that can be easily melted and
become sealed. If it needs to vent at any point in the future the cell
may explode! This is the reason we weld the cells. I would tend to cut
the strips at the centre and solder wires to the remaining stubs.
BTW the Ryobi 2 pack of 18V batteries sold at HD is a good cheap source
I think soldering cells together may be trickier than what meets the eye.
IIRC the biggest trick is to not heat the cell up when you solder the
connections. The heat build up damages the battery if the connection does
not take very quickly.
You don't solder them together, you spot weld them. Spot welding localises
the heat and it's much faster. Find a weldor and bring him or her a cold
six pack and a ten spot, you're still better off.
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