Li-ion AAA replacement with li-ion pack

[clearchris]

Ok, I have this device, a skulpt chisel. It's acting funky, and the battery never goes higher than 70% charged anymore. I popped the case open, and instead of NiMH batteries I was expecting (older version had them), I found Li-ion batteries. Two 10440 AAA form factor 3.7v 320mah batteries. I can find 10440 batteries, but finding ones with solder tabs is a challenge. I'm really not into ebay li-ion batteries. I'm not soldering the tabs on myself, it's not worth the risk.

So, I have found a flat pack that will fit. I can cut the plug, solder the wires on, tape the pack down, and it's all good.

https://www.adafruit.com/product/258

My question is, will the electronic protection circuits on this pack interfere with the charging circuits on the board? The standard li-ion AAA batteries don't seem to have any obvious protection circuits on them.

Thanks!

Battery Datasheet:
https://cdn-shop.adafruit.com/produc...ROVED_8.18.pdf

Battery Protection IC
https://www.ablic.com/en/doc/datashe...on/S8261_E.pdf

And there is an 8814 mosfet which i assume cuts off the battery if something bad happens.

skulptboard.jpg

[momaka]

If these two current Li-ion AAA batteries are in parallel there without any protection... oh boy!

I don't imagine the Li-ion pack with protection will have issues with the charging circuit, but I'm not an expert in this area. Will wait for someone else with more experience to chime in here.

[clearchris]

They do appear to be in parallel, but from my readings on li-ion charging it's not neccessarily a problem. You have to build a "balance" phase into the charging. At any rate, I think I'm going to a single cell pack, so it should be safer in that regard.

[sam_sam_sam]

Originally Posted by clearchris

So, I have found a flat pack that will fit. I can cut the plug, solder the wires on, tape the pack down, and it's all good.

https://www.adafruit.com/product/258

My question is, will the electronic protection circuits on this pack interfere with the charging circuits on the board? The standard li-ion AAA batteries don't seem to have any obvious protection circuits on them.

Thanks

Attachment 182610

You should be fine with this battery but do not remove the protection board
Unless the unit requires a different cut off voltage to the batteries then that could be a problem I have only seen this a couple of times
Your unit should work fine with it

[petehall347]

recycle the charge fully 3 times and see what happens.

[clearchris]

So far, so good. It's reading 94% charged, which is better than the 70% charged the old batteries would show. I don't know that it will ever be fully cycled, it gets used for a few minutes and put back on the charger. I could leave it off the charger for a few weeks, if you guys think that it would be helpful to fully cycle it.

I put double sided tape on the top to stick it to the top case and same tape on the bottom to protect the battery in case it gets loose. There was a lot of room left, I could have easily used a larger battery.

Overall, this was a pretty easy fix. The case came apart with a plastic pry tool, there was no breakage, the clips seemed stout. I cut the batteries off with some side cutters so I could use as much heat as needed to remove the tabs from the board.

We'll see how this battery holds up.

Thanks to everyone!

skulpt-fixed.jpg

[momaka]

Good to hear it's working. As a bonus, you also have a slightly upgraded capacity from before as well (1x 850 mA battery vs. the old 2x 320 mA, which didn't even charge fully).

[sam_sam_sam]

What is your voltage when it says 94 % this might be a problem with having two protection board on the unit if your voltage to the battery is 4.2-something you’ll be alright you just have to remember that when it says 94% mean that it fully changed

[clearchris]

Originally Posted by momaka

Good to hear it's working. As a bonus, you also have a slightly upgraded capacity from before as well (1x 850 mA battery vs. the old 2x 320 mA, which didn't even charge fully).

Yep. IIRC, I have never seen it at 100% even when new. I checked yesterday and it read 97%. I don't ever believe the stated rating, but my new no-name battery probably does have more mA vs the original no-name batteries.

I'll probably have to swap them out again in a year or two, at that time, I'll see what the biggest battery I can fit in there is. It's kind of overkill though, it lives on the charger, gets taken off for 5 minutes and goes back on the charger.

[clearchris]

Originally Posted by sam_sam_sam

What is your voltage when it says 94 % this might be a problem with having two protection board on the unit if your voltage to the battery is 4.2-something you’ll be alright you just have to remember that when it says 94% mean that it fully changed

It could be, though from the spec sheets I read, these chips have very little draw. I did later get a reading of 97%, so I'm optimistic about that.

Not sure what the voltage is, but the 70% charged batteries were at 4.1v, which was surprising to me, I wouldn't have thought that from 4.2v to 4.1v was a 30% drop, but I haven't reseached the voltage drop curve of li-ion batteries.

[momaka]

Originally Posted by clearchris

I'll probably have to swap them out again in a year or two, at that time, I'll see what the biggest battery I can fit in there is. It's kind of overkill though, it lives on the charger, gets taken off for 5 minutes and goes back on the charger.

Ah, that's a good way to kill your Lithium batteries - keeping them close to 100% charged all the time.
If you want your batteries to last, keep them between 25% and 75% most of the time, and only fully charge when needed.

[sam_sam_sam]

Originally Posted by clearchris

I did later get a reading of 97%

Not sure what the voltage is, but the 70% charged batteries were at 4.1v, which was surprising to me

I am not surprised by your results the battery charger that I have show the same type results and most cell phone battery backup have the same type of results

I try not to run down a lin-ion battery below 40% very often I find that the batteries do not seem to last as long as when they are new

[clearchris]

Originally Posted by momaka

Ah, that's a good way to kill your Lithium batteries - keeping them close to 100% charged all the time.
If you want your batteries to last, keep them between 25% and 75% most of the time, and only fully charge when needed.

That presents quite the conundrum. The device doesn't function well at around 70% battery or lower. I don't think it deals well with the voltage sag. The bluetooth connection barely works, I have to hold the phone within 6 inches of the device.

So I guess I'm back to leaving it on the charger and replacing every few years. Maybe a larger battery would work better, it would be able to have higher voltage for longer, and I could leave it off the charger.

sam_sam_sam:

Yeah, I guess the batteries stay high voltage for longer, and then lose voltage quickly. I assumed a more linear voltage drop during discharge.

[momaka]

Originally Posted by clearchris

That presents quite the conundrum. The device doesn't function well at around 70% battery or lower. I don't think it deals well with the voltage sag. The bluetooth connection barely works, I have to hold the phone within 6 inches of the device.

Sounds like it was designed for a 3.6V Ni-Cd or Ni-MH battery pack (3x 1.2V cells, which normally come out to around 4.4V charged) or perhaps even a 4.8V pack (about 5.8V when fully charged).

I suppose there isn't much you can do then. For a moment, I thought perhaps a cheap boost converter in there would do the trick. But with that running all the time, this will drain the battery by itself too. Battery charge also won't last as long due to some efficiency lost in the converter. So that's probably a no-go either.