Why did I get this phone? I had one back in the day, plus I'm finding using a modern smart phone too distracting. Current minimal GSM devices still have too many unneeded functions and gadgets, they are also short on comfort and are too fiddly for my hands. These old Ericsson phones can be bought for little money from the usual sources, they come as standard with batteries in need of fixing / upgrading.

These phones are really easy to work on, 4 screws and you've got the back off, 3 more and the pcb comes out. I did my usual thing of ripping through the battery cell change without thinking to take any photos. Getting into the battery was a simple case of using a spudger. The cells I used were from an old radio controlled glider project, and were AAA Nimh type batteries. 

My next used battery will have a USB charge port on it, also will remember to take photos of the build. After replacing screens on a Sony Android phone that was basically glued together, the Ericsson GA628 is an absolute joy to work on. It's designed to be fixed, something that is getting worse and worse with the current crop of glass clad smartphones imho.

I have a couple of 28850 lithium cells spare, left over from a torch that let all its magic smoke out. May use a one with a 3D printed back, to create a nice curved profile for better comfort, if I can find enough PLA.

Hmm.. it's difficult to get the extended battery apart. May just design and print a custom battery enclosure.

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Ok, so now the design is started, I will publish STL files and maybe the drawing files when I'm finished with the design phase of this project.

May need to use a different method for attaching the battery, maybe a magnetic catch to get rid of the horrid standard lower catch. This will involve drilling the metal chassis and gluing in small but powerful magnets. Meanwhile, I'll print and see.

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Good, now I've done everyone else prints on my cheap Prusa i3 clone, maybe I can start actually building something.

I ordered a 2600 mah Nimh battery for a radio controlled model, it's built from 4 AA cells, which add up to a nominal 4.8 volts. Once stripped of shrink wrap, the pack folds out to make an ideal replacement! I'll use one of my Arduino clone boards to log the voltage of the pack while it charges. The other AAA battery I build for the GA628 doesn't seem to have the capacity it first had. The only way to find out what's going on, is to measure it. The Arduino will be connected to my workshop computer via USB, then I'll use 'screen' to monitor the output voltage, eventually making a spreadsheet of the results. Don't want to buy an expensive data logger for this low cost project, besides... why buy when you can make!

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Trying to make this thing simpler, maybe use a DC/DC converter to get 5 volts from a 18650 cell. I don't need a charging controller, if I use removable 18650's and charge them with my usual multi charger, then no need for a USB socket.

I think I've talked myself out of using a 18650.

I just need a 4 x AA battery holder, and a method of mounting it onto the phone. This way, I can use disposable AA batteries and have an emergency cell phone. The AA battery holder doesn't even to be removable and could be soldered onto the power contacts.

Sometimes, a project just evolves and changes.