2 batteries in parallel in a new case?

[Matthieu]

Considering the small capacity of FP2 battery, I was wondering if anybody had tried to wire two (or more) of them in parallel, maybe encased in a 3D-printed case?

I know people have done that with Samsung batteries, but batteries nowadays have some embedded electronics to give information to phones, so I’m guessing it’s not as easy as “solder both plus and minus together and here you are”.

If it is technically possible, it could be feasible to have an extra layer of a 6-8mm in a 3D printed case containing 2 extra batteries.

Or we could have a regular accumulator connected to the 5-pins USB-backport?

[urs_lesse]

Have a look here:

Larger capacity FP2 battery

Hi Folks, I’ve been owning a FP2 for nearly a year now. One of the first things I remarked was the lack of battery power. So a friend and me decides to find a way to put more juice into it. The design is intended to: meet safety regulations by taking the hardware of an existing battery case for another phone Add heat sink capacity by including a 1€ coin above the CPU maintain one unique external USB port for charging (both battery and phone) and data access cost less than 50€ in total We fo…

Not sure if there is wiring though.

[Matthieu]

Thanks, almost exactly what I was looking for! More details are given in the original page. The KiwiBird is used as the extra battery pack so I guess Samsung was the one soldering

[ElKrasso]

Beauty is in the eye of the beholder, but one must be blind.

[ThinkTwice]

Hi @Matthieu!

Several people have been working of similar stuff:
Here was a discussion on how to connect n extra battery to the USB debug connector

Doubling the battery capacity by soldering two stock batteries together has been tempted here. BUT this has one huge safety drawback as neither the battery Protective Circuit Board (PCB) nor the FP charging circuit will be designed to handle higher load. And, most importantly, if you connect two battery cells together without charge balancing, you may end up with thermal runaway (if one battery charges the other one because of slightly different voltage, you will burn both of them), which might lead to serious injury (see here).

@jayy has been working on a circuit for using standard 18650 cells over here, but I don’t know whether that project has been continuedhttps://forum.fairphone.com/t/2-batteries-in-parallel-in-a-new-case/49374/2

@ElKrasso sure I didn’t optimize visual design, as I first and foremost needed a working prototype in order to get more juice into my FP2. If you’re in for remixing my design ( all files are posted on thingiverse), go ahead, I’d be pleased printing your version!

Btw I’ve been gathering charge stats for several months now. I’ll try to compile and analyze them within the next few week to see how much this actually gained, but roughly I got 2,5 original charges with the battery extension.

@urs_lesse : no wiring needed (if you manage to not cut the wires betwen both boards when unmounting them from the original case). The electric circuitry is kept from the original.