Quick iBook (clamshell) battery rebuild method

[zigzagjoe]

I've got a clamshell with a dying OEM battery, time to rebuild it. Turns out it's quite annoying to get 18650 cells with presoldered tabs, and I don't have a spot welder. Ugh.

So instead I had the thought: why not cannibalize some chinese laptop replacement batteries for those cells? It's likely not the best quality cells, but I just want *some* battery functionality rather than caring if it eeks out exact as-new battery life. I'll balance it a few times with my hobby lipo charger as I don't trust that it's been well-balanced beforehand; this is often why packs die prematurely. I'll also get to see just how much capacity these cells actually have.

Taking it one step further: the Ibook battery is just a 2P4S (two cells in parallel x 4) pack .... a very common topology. Why not just get a chinese battery already in that configuration and skip needing to solder cells together at all? If that works out, I'll have a refurbished iBook battery for $30!

One chinese battery ordered, and promptly shucked. Here's what's inside. Plenty of flex on the solder tabs, I think it should drop right into the iBook with some kapton tape to insulate where needed. I've soldered a balance lead to the battery in the picture here.



It'll be a few days to discharge and balance it a few times before I install it into the pack, will update with results...

 

[davidg5678]

Very interesting idea! I'll be following this

 

[zigzagjoe]

I'm getting a measured capacity of ~4500 mAH, where the cells are marked 2600 mAH capacity. Not terrible. Balance is... adequate. 3 pairs of cells are well balanced, but the last pair on the positive side of the pack is consistently riding high. So when the other cells hit 2.9v, it's still at 3.3v. That's not ideal, but I think it'll be fine as long as I avoid fully discharging the battery. Of course, I will need to do that to calibrate capacity... c'est la vie.

Going to proceed to build the battery tomorrow. One of the solder tabs on the new battery let go at some point as I was removing it/adding balance leads, but I was able to tack it back with solder.

NB: Don't solder tabs to batteries if you can avoid it, and if you must solder it (ie. no spot welder) solder extremely quickly with lots of heat and lots of flux. I heated the joint for maybe a second.

 

[zigzagjoe]

Got it all assembled. Had to dremel off some bits inside the ibook battery plastic, but eventually got it all to fit well enough. I could only partially snap it together, but it is close enough with a bit of transformer tape to hold the reticent bits closed. Discharged it once to calibrate and recharged, balance looked good after the ibook reported 100% charge and it lasted for a bit over 5 hours at the boot menu. I'll call it a win!

 

[KnobsNSwitches]

What a great idea. I've never disassmbled an iBook battery before - is the wiring straightforward with the new cells?

 

[zigzagjoe]

What a great idea. I've never disassmbled an iBook battery before - is the wiring straightforward with the new cells?

The cells are already wired exactly as they need to be, so it's just a matter of wiring up the ibook connector/BMS board directly to the new ones and then mechanically making it fit.

 

[ArjenCNX]

I found that if you want to disassemble the battery, it is helpful to remove the top and bottom stickers first, they peel right off, then you can use a spudger between the battery and the housing and apply pressure as you pry it open. its still a shitty job, as your battling glue and clips at the same time, but it does seem to work quite a bit better. Using a (cheap) spot-welder for the cells is a must in this re-build, they can be had for little money. where also attempting here to make a 3D printable battery housing for this, it's a work in progress but will be shared once done.