I have an old favourite Makita 6v cordless drill/driver that is no longer
taking a charge. The batteries are of the semi-permanent NiCd variety. I
can't find a replacement for them so I was thinking of making my own battery
pack out of AA rechargeable batteries. Easy enough to solder together 4
The question is, can I use NiMH batteries instead of the original NiCd? If
I do, will the original AC charger work to charge up the NiMHs? I'm not
sure how the two battery types differ in terms of charging needs.
I have used a rebuild service. They have done an 18v and 2 12vs for me.
Upgrading to NMH on the process IIRC.
I'n not affiliated with them but have used their service. Their website and
order process stinks but they got the job done.
Here's what I know so far (and please somebody correct me if I'm
NiCds and NiMH have different charging characteristics. Smart
chargers for NiCds usually use negative delta-v detection to sense
when the battery is charged. In other words, when a NiCd cell reaches
capacity its voltage actually drops a bit, the smart charger senses
this and stops charging.
When NiMH reach capacity they can go either negative delta-v or zero
delta-v, so it depends on the cell. I think they also rise in
temperature, so you have chargers that may detect this rise in
temperature and stop charging.
NiCds can tolerate bigger current draw and are more tolerant to
overcharging (if using a 'dumb' trickle-type charger). I also think
you get more recharge cycles for NiCd than for NiMH. NiCds also work
better in the cold although this may not be applicable to you.
You may want to look into the required charging current for the NiMH
cells you are considering to see if your charger is compatible. You
have to charge the cells at their rated capacity, in other words if
the cells are rated 1500mAh you need a 1.5 amp charging current for a
As for soldering cells, you can do so but be very very quick, don't
let the cell heat up or you'll damage them. Use a soldering iron with
a wide tip so you have enough surface for a good and quick heat
transfer; you may need to hold a smaller iron longer and this may
damage the cells. I use dad's old Fuller 50W with a quarter inch tip.
Use the copper braid from a old length of coax cable to connect them,
then use heat shrink tubing to package them up. Start by shrinking
the ends first then the middle so the pack will be tighter.
To make a long story short, try to find NiCds with the same
characteristics as the old cells.
I think you and I are working on a similar project: I'm looking to
build a battery pack for a bike light, either NiCd or NiMH (I'm very
much leaning on NiCd), and I'm looking to built it myself using
7000mAh D-cells. I'll be using a modified DeWalt 9107 (smart) charger
to charge 'em up.
===> Nothing to correct; that's a pretty good writeup!
Basically, for the OP, try to stick with the same
battery type as the charger is/was meant for; you'll
get better and more reliable use of the batteries.
Batteries care about their charging rates for their
longest life. "Better" batteries without the proper
charging specs could, not will, result in a short
charging life. Charging voltages (and thus rate of
charge) varies with the type of battery.
Another tip for soldering: lightly sand the battery
solder locations wiht a high grit sandpaper (220 is
good) and wipe down with medicine-cabinet alcohol; do
not touch the solder surfaces with your fingers.
And do solder as reasonably quickly as you can. If
you flub it, wait ofr the battery to completely cool
inside before you apply heat again. Batteries store
heat for several minutes.
But his drill I assume comes with a charger. In this case he would no
longer be able to use this charger correct? That would be a bad idea
since Im sure the battery caseing and whatnot is designed specifically
for this charger.
I would stick with the same battery type, there is no reason to change
While the other posters who mentioned different charging rates are correct,
there's also the issue of discharge rate. NiMH batteries have pretty good
discharge rates, but not quite as much as NiCd. This is important, because
those power tools demand a lot of power. While in this case the difference
isn't huge, it may be enough to underpower your drill, shortening your
battery life as well as the life of the drill.
Also, NiMH batteries don't hold their charge very well. You can pick up a
NiCd battery after several weeks and expect it to be near fully charged.
NiMH batteries will be stone cold dead in a month, which brings another
issue, which is one cell will almost surely die completely or have it's life
seriously shortened with a full discharge. The weakest battery will be
drained first, and the others will send a reverse current through it, which
It's best if you stick with NiCd.
As an aside, you can buy these things with the tabs already soldered on.
Soldering directly onto battery terminals is a big pain. The price
difference is insignificant.
If you are like me, I don't give much thought to charging rates, and decline
rates, and interest rates. I just want to know that my batteries are gonna
work. There's nothing like going to do something, and your batteries are
Right now, I have three Makita 9000 9.6 batteries. I would rate one an 8,
one a 6, and one a 3. It is time to get new ones, but hell, they cost as
much as a new drill. With batteries. AND charger.
Think I will bite the bullet this time and get a DeWalt.18v. I really like
the little Makita, but no sense spending money on something that is going to
crap out at any time.
Don't be too quick with that. I know a few unhappy DeWalt owners due to
clutch problems. Our maintenance supervisor just dumped his DeWalt in favor
of a Craftsman. I don't know if it was this group or the woodworking groups
where there were recent complaints about the ability to set the torque for
Thank you for the heads up. I have seen some pretty good deals on Craftsman
minigloat - I picked up a new set of 42444 Craftsman ratchet wrenches at the
Oceanside, California Swap Meet last weekend for $25.
I have a Bosch 14.4 drill and am very
happy with it. The nice feature is that
you don't have to use 2 hands to tighten
the chuck. The motor/gear has a lock
when off, so you only tighten it with
one hand. I also bought one for my son.
I also bought a Craftsman 19.somthing
volt kit with drill, recip saw, circular
saw and light for my son. This kit is
real nice and is very powerful. I was
even thinking of getting one for me,
however, I have most of the tools
already. But, my "Tool Shop" recip is a
poor excuse for a tool. It vibrates
wildly, is pretty weak and the battery
doesn't last. I gues that's why they
are that cheap. I do, however, like my
18 volt DeWalt circular saw. It is
really a great tool.
My Craftsman batteries are powerful, but was surprised to see they
only used sanyo kr-1300sc nicad battery cells.
In an earlier thread.
" That's ok, but I hated adding less powerful cells to my better
so decided to order some powerful new 1.2 V cells that are even better
than what they replace. I got them at
They sell very powerful nicad cells that are double the power of the
standard Craftsman cells. And they come with solder tabs at no extra
If you want to add power, put the batteries in parallel. If you have
enough space, you will double the power and/or usage time of your
'battery pack.' Perhaps that is what these 'powerful' cells have,
parallel cells inside 1 unit.
On Mon, 11 Jul 2005 09:31:38 -0400, "CL (dnoyeB) Gilbert"
Oh, don't even think about that. The packs are chock full of
batteries and not room for even an extra AA.
I replaced the a couple of 1300mah with 1800mah and can tell the
difference already. Next, I'm gonna do the spot light.
NiMH discharges at about twice the rate of NiCd. That is nowhere near as
bad as you claim. As well, topping up NiMH is easy, whereas partial
discharge gives problems with NiCd unless you have a conditioning charger.
If you use the tool a lot on a continual basis, NiCd is the way to go.
If you use it occasionally, NiMH wll be better, though you may have to
top up the charge first. If you've got loads of money, Li Ion is better
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