[shrek]

I have a few G4 laptops with worn out batteries that need a rebuild with fresh cells. I'm a tad nervous about soldering directly to the terminals but I think it'll be okay as long as I don't keep the iron on it too long. 

Can someone who knows what they're doing give me a little help with purchasing parts? I don't know anything about batteries. Is it okay to use the highest capacity batteries I can buy or should I try to match the originals? What other specs should I look for?

[robespierre]

The cells should be replaced with the same chemistry as the BMS (battery management system) is programmed for that specific voltage/charge curve.
The original cells were NMC chemistry types like the Sony US18650GR, so they should be replaced with NMC 18650s without a button or internal protection, and with partial wrap (exposed ends) because that saves the step of cutting the wrap back to attach the tabs.
Suggest you use a tab welder and not a soldering iron because it is rather difficult to solder to the cells. NMC is not likely to explode but any extended heating will damage them and reduce capacity/life.

This user was successful in soldering replacements, but he used sets from Dell batteries with tabs already attached in the right manner (2P4S). You might be able to find cells with preattached tabs somewhere.
http://www.neufeld.newton.ks.us/electronics/?p=149

[shrek]

The cells should be replaced with the same chemistry as the BMS (battery management system) is programmed for that specific voltage/charge curve.
The original cells were NMC chemistry types like the Sony US18650GR, so they should be replaced with NMC 18650s without a button or internal protection, and with partial wrap (exposed ends) because that saves the step of cutting the wrap back to attach the tabs.
Suggest you use a tab welder and not a soldering iron because it is rather difficult to solder to the cells. NMC is not likely to explode but any extended heating will damage them and reduce capacity/life.

This user was successful in soldering replacements, but he used sets from Dell batteries with tabs already attached in the right manner (2P4S). You might be able to find cells with preattached tabs somewhere.
http://www.neufeld.newton.ks.us/electronics/?p=149

Thanks for the info. Do you know where I could get the Sony cells you mentioned? I looked around found some used ones but they're listed as Lithium Ion G8 and they don't mention NMC. Those are here:   https://higherwireenergy.com/products/so...0mah-rated

My PowerBook battery is also a lot different than the one from the article you linked. I don't know if that makes a difference. It's one of the later models with a 1.67GHz CPU.

I managed to get it open with minimal damage to the casing. I don't want to spend the extra money on a tab welder machine so once I get the parts I will just try to do the repair with a soldering iron.

[robespierre]

The specific brand isn't important (although don't buy UltraFire or anything else named after a fire).
You simply can't solder with normal methods to a battery case, it's made of stainless steel. Look for cells with tabs preattached.

[shrek]

Thanks for all the help. Unfortunately I think for now I have to shelve this project because the cells with tabs are more expensive, so the cost of materials will be close to a new aftermarket battery from Amazon. I don't even know if the DIY repair will work.

Maybe in a few years when my other laptops heave dead battery packs and no cheap replacements I'll invest in a tab welder.

[ghost180sx]

for what it's worth, I have a 15" PowerBook G4 Aluminum (1.5GHz) and bought an aftermarket battery off of Amazon. The battery, after only 19 cycles, has dropped to 70% of rated (4400 mAh) capacity. It's now around 3000 mAh. You might decided to still buy your own cells...

My friend has a battery tab welder. He paid $200 for. It's a chinese model, but I've already built a NiCAD battery pack for my vintage 486 portable, re-cycling old cordless drill batteries, and it worked great. Maybe a friend or local maker space can get you access to a tab welder?

[robespierre]

My friend has a battery tab welder. He paid $200 for. It's a chinese model, but I've already built a NiCAD battery pack for my vintage 486 portable, re-cycling old cordless drill batteries, and it worked great. Maybe a friend or local maker space can get you access to a tab welder?

DIYers sometimes improvise tab welders from re-wound microwave oven transformers and copper nails.
If I was going to buy one, I'd get this: https://www.keenlab.de/index.php/portfolio-item/kweld/

It's also possible to solder to stainless steel using special acid fluxes. Superior Flux & Mfg Co. makes several that will work, Superior No. 79 looks like one of the safer ones (no zinc chloride). You also need to use a sharp tip (like a carbide drill) to scratch the steel to make a dent in the oxide layer.