NiMh-NiCd Battery Chargers--Can They Be Converted To Charge Lithium Li-ION Batteries ?

The reason I’m asking this question , is while looking

on Craigslist for Lithium Battery Power Tool Packs, I

saw an ad for Lithium Battery Packs for sale. Also for

sale was a NiMh battery tool charger. The owner

stated, he could make the charger work on Lithium

batteries. He just had to remove some plastic from

somewhere on the charger, to expose some part on it.

Is it possible by chance ? It sounds crazy, but what

do you think ? :~

Big fat NO!

Doesn’t sound likely. NiMh/NiCd chargers are pretty simple devices compared to Li-Ion chargers. There are generally two approaches to NiMh/NiCd chargers.
Dumb chargers that charge at a rate of C/10 or less (these devices don’t ever stop charging), and more sophisticated chargers that look for DeltaV and usually charge at something around .3-.5C.
As a NiCd or NiMh battery reaches capacity there is small drop in voltage across the cell. This is signal to either stop charging, or change over to a trickle charging. Over charging a NiMh or NICd cell just shortens the life a little. over discharge (as long there is no ‘reverse’ chargine, NiMh and NiCd cells are pretty tolerant of. Charging NiMh or NiCd cells in series is quite acceptable and safe. Definitely not recommended for Li-Ion cells.

Li-Ion cell charging is done entirely differently, and Li-Ion cells do very ugly things if you overdischarge them, or over charge them. In the first part of
the charging cycle, a fixed current is used, as the battery approaches capacity, the fixed current changes to a fixed voltage, The battery is considered fully charged when current in the fixed voltage charge falls below 10% of the original fixed current charge.So if YOu charged at 500ma, the cutoff will be when
at the fixed voltage, the current is 50ma or less. In addition if you are using protected cells, the charger usually will also reset the protecton by
initially charging at very low current.

While there are chargers that can do both, it involves two sets of electronics in the charger and usually a microprocessor to figure out what type of battery you have put in the charger.

if the charge rate is very slow, one could charge any battery with it imho

Not true. Get the NiMh/NiCd charge rate below about C/20 and they never reach full charge. Discovered that the hard way on a project where we wanted to optimize battery life. We did get excellent life, but the down side was we could never charge the battery up enough to get anywhere near the rated capacity out of it.

It is just a bad idea to knowlingly over charge Li=Ion cells, no matter how slowly you do it.

So it’s not possible to make a NiMh charger work to

charge a Li-Ion battery ?

You could probably make use of many of the parts, but you’d end up hacking the hell out of the electronics.

With probably 2x the cost and 15x the work to just go out and buy one.
TOTALLY different chemistry. TOTALLY different charging method. Excellent way to end up with a small bomb.

Yeah, sure, IF you want to load it down with ACCURATE diagnostic monitoring, AND sit there watching while it charges so it doesn’t overcharge and burn/blow up……the WHOLE time.

Not a good idea at all.

If you are asking then the answer is no. (very blunt, I realize)

Purge the idea from your mind. There are some very inexpensive high quality options available. RMM carries quality XTAR single-cell chargers for <$10 shipped (the SupFire has yet to be proven by HKJ - I rarely buy a charger without looking at his reviews). A two-cell Nitecore i2 (also quality) is only $12.35 directly from Amazon, although you’ve got to jump through the usual Amazon hoops to get free shipping. The Xtar XP4c is <$25 shipped from RMM and takes 4 cells. EDIT: sorry for not paying close enough attention - you want to charge packs. Those options are not good for packs. The rest of this post is still imparting exactly the message I want it to - stick with the manufacturer’s recommended charger unless you have technical knowledge which leads you to do otherwise. Anecdotal stuff should not be enough to make you feel comfortable.

You’ve probably already used “search” and found no easy solutions to charging Li-Ion w/ NiMH chargers. That’s because an easy solution doesn’t exist. A hard solution is both expensive and a very bad thing if you aren’t already very knowledgeable about both batteries and circuit-level electronics.

Long ago a variety of circumstances came up at the same time where it briefly made sense to re-use powerful RC NiMH chargers in that way. Dan Baldwin made the Terminator circuit to facilitate this. His Terminator cost $40. That was on top of the cost of your existing charger! Hopefully this will give you an idea of why I’m trying to steer you away from the concept.

don’t agree

you can get a very cheap charging module for LiIon, and put it into the housing of the original charger, so you can use the original charging craddle. You reuse the housing, replace the electronics.

If you want balancing, you can get balancer charger for cca 10$, and hook it up in the original craddle.

If you still need a charger, I highly suggest checking ebay or amazon for the original MFG charger designed for your packs. You can oftentimes find the original charger for less than $30 shipped depending on what tool you’re using.

In answer to your OP, yes, on some chargers, you can remove/add a contact, and make it so you can charge different chemistry.

Should you? NO. they are different chemistry, they each need a different charge pattern.

That’s pretty funny, had my laugh of the day, thanks!

I’m not going to try to convert the NiMh charger to
work on Li-Ion batteries. Read my OP-In a craigslist
ad, someone was selling Lithium Tool Pack batteries.
He did not have a lithium charger for the batteries, but
he had a NiMh charger(also 4sale) which he claimed he
could make it work to charge the Lithium battery tool
packs by removing some plastic from somewhere on the
NiHm charger !—I didn’t know if it’s somehow possible !

Are you saying that you’re more concerned about the integrity of these batteries after this dude has done this to them?

If so that’s a good point - I’d skip the batteries he’s had his hands on!

So your answer is basically Yes , it can be done in certain
ways and means.—-But safely, NO ! Am I somehow correct
in my interpretation of your statement ? :~

it can be done if you replace the electronics, but if your going to do that then just buy the right charger

My OP was to find out if the charger mod was possible.
I’m not sure if he’d already modified the NiMh charger
and charged the lithium batteries that he had , when
he placed the CL ad. In ad he stated “he could make”
the charger work by removing some plastic from
somewhere on the charger. I guess it depends on
one’s interpretation of his statements. You are
probably right about surely ” skipping his batteries”.

My interpretation is he is going to remove the safety tabs, which were specifically designed to physically prevent incompatible battery packs from being inserted into the charger. If the charger was really multi-chemistry compatible, it wouldn’t need the safety tabs.

Do you have a tool that uses these battery packs or are you simply after the cells?