You can definitely do it, but the price for 4/3A NIMH batteries isn't too different from AA's when you go for the cheapest compared to original Sanyos. You can get a 10-pack of generic 4/3As from china for 22$, but you have to understand that they have a tendency to lie unscrupulously about the capacity. If it says 3800mah it's likely to be something like 1400-2000mah actual, and i wouldn't be surprised if Amazon Basics ones are the same.

https://www.aliexpress.com/item/10Pcs-1-2v-4- … 2412555871.html

As for the charging circuitry i doubt it's smart enough to keep track of capacity, after all the batteries are going to lose their capacity over time through daily use.

Nprod wrote:

You can definitely do it, but the price for 4/3A NIMH batteries isn't too different from AA's when you go for the cheapest compared to original Sanyos. You can get a 10-pack of generic 4/3As from china for 22$, but you have to understand that they have a tendency to lie unscrupulously about the capacity. If it says 3800mah it's likely to be something like 1400-2000mah actual, and i wouldn't be surprised if Amazon Basics ones are the same.

https://www.aliexpress.com/item/10Pcs-1-2v-4- … 2412555871.html

As for the charging circuitry i doubt it's smart enough to keep track of capacity, after all the batteries are going to lose their capacity over time through daily use.

The problem with industrial sized batteries is that you need to find someway of connecting them together - soldering tagged batteries takes up space in the pack, so you end up having to spot weld.

I've got a NiMH laptop "on hold", with the battery pack split apart - 8 off 4/3AA batteries. My game plan is to replace with two 4xAA holders, initially using some spare/knackered "2500mAh more like 1500mAh mate" cells I have lying around, and if it works, I'll look out for some low self discharge cells - I would expect to pay about £10 (GBP) including shipping (=18CAD/13USD).

I've already worked out the diagram for the builtin charger controller - matches the data sheet, but it looks as if the battery pack itself has reversed polarity, so I decided to "reprioritise" and park it for the time being. (This laptop had a LiIon/NiMH option - the charger controller being built into the battery pack).

Soldering them together directly by the leads is not impossible, i've done it for a cordless drill's battery pack, using lead-free solder even. What you do is you rough up the surface with sandpaper first, add a drop of flux and then solder on a bead using a large tip on the iron (holding it on no longer than 2-3 seconds). Using AA battery holders makes future swaps easier but that's about it. The easiest thing to do is get a pre-packaged 9.6V bundle (or a 12V one in metricmoose's case) for an RC car, they come with a convenient connector too.

Nprod wrote:

Soldering them together directly by the leads is not impossible, i've done it for a cordless drill's battery pack, using lead-free solder even. What you do is you rough up the surface with sandpaper first, add a drop of flux and then solder on a bead using a large tip on the iron (holding it on no longer than 2-3 seconds). Using AA battery holders makes future swaps easier but that's about it. The easiest thing to do is get a pre-packaged 9.6V bundle (or a 12V one in metricmoose's case) for an RC car, they come with a convenient connector too.

That's ok for side by side connections between two batteries located "II" but I was thinking about batteries in line "--" in a cramped box where any strap between batteries needs to be within the diameter of the battery and as thin as possible - the only additional thickness with a spot welded strap is caused by the thickness of the bend. With a pair of batteries with prewelded tags, the thickness is determined by the solder blob holding the two tags together, and with untagged cells you have two solder blobs.

It might only add a couple of millimetres, but combine that with the fact that you could have 2mm tolerance in length between two batteries from different manufacturers, and you could end up running out of space.

Nprod wrote:

You can definitely do it, but the price for 4/3A NIMH batteries isn't too different from AA's when you go for the cheapest compared to original Sanyos. You can get a 10-pack of generic 4/3As from china for 22$, but you have to understand that they have a tendency to lie unscrupulously about the capacity. If it says 3800mah it's likely to be something like 1400-2000mah actual, and i wouldn't be surprised if Amazon Basics ones are the same.

https://www.aliexpress.com/item/10Pcs-1-2v-4- … 2412555871.html

As for the charging circuitry i doubt it's smart enough to keep track of capacity, after all the batteries are going to lose their capacity over time through daily use.

Thanks! I didn't think to check Aliexpress, unfortunately it looks like the shipping is going to be $35 on those batteries and I couldn't find a better deal than that. I also dug around Aliexpress some more and found a pre-wrapped 12V Ni-MH pack, but it was listed as only 1.8Ah, which wasn't too inspiring. So I ended up buying a 10xAA holder for three bucks on eBay and I'll order the 8 pack of AmazonBasics 2.4Ah AAs. The dimensions on the pack seem just about right, though the height might be cutting it close. I guess I'll find soon enough!

Hint: Ikea rechargeables are supposed to be relabeled eneloops.
https://gizmodo.com/are-ikeas-7-rechargeable- … -ene-1823204061

That's ok for side by side connections between two batteries located "II" but I was thinking about batteries in line "--" in a cramped box

Oh yeah, inline is going to be difficult... Did the original pack have them spot-welded end to end?

So I ended up buying a 10xAA holder for three bucks on eBay and I'll order the 8 pack of AmazonBasics 2.4Ah AAs.

Why an 8-pack, don't you need 10 of them?

Hint: Ikea rechargeables are supposed to be relabeled eneloops.

Neat! I'll have to remember to look for them next time i'm there.

As Nprod said, just solder the batteries.
The crucial thing is to keep the actual heating as short as possible and the solder blob placed and sized in a way it does not disturb.
An 1mm solder blob at about 1/4 diameter into the inside of the battery is best, where you can solder at the side of the battery "pin". Just as large as necessary for a good connection and placed that it won't increase the length of the battery chain.

Exercise this using dead batteries. You must be quick. 2-3 seconds are sufficient to damage/degrade batteries, so hone your skill that you can make it in less than one second. (Hint: Iron must be hot, I have set it to 450 degs C, and tin must be leaded and have good quality flux core. Soldering station must have some minimum power too, maybe 50+ watts)