DIY battery bank phone case. How to do this?

[Love.Sun]

My apologies if this is the wrong forum to ask..


But, I would like to DIY a phone case with a built-in additional battery. Preferably Li-Po because they are flat in shape.

I don't want to remove my original phone battery. It's new and works well.

I just want to take a power bank concept and combine it with a silicone phone case in a more efficient manner. I can buy a bulky power bank and carry it around separately from the phone and plug it in to charge the phone when necessary, but that's rather inconvenient.

Instead, I'd like to have a phone case with the second battery in it, and for that case to have a USB-C port so that when I place my phone in the case, it automatically connects with the second battery, which starts charging the internal battery.

Next, I'd like to be able to charge both batteries at once. So that the external battery in the case has its own USB-C charging port where I can charge the second battery, which in turn charges the internal phone battery. That way, both batteries are charging at once. Right?

Is this possible? What would I need to do to make this? Is there a BMS needed for this?

Thanks everyone who wishes to help! Looking forward to your comments ?

 

[A.Justice]

Check out BatteryHookup.com. They sell used li-po "flat packs" for almost nothing, and most of them have a BMS installed. I would prefer a Li-po pouch cell that has a hard case, and BMS from the factory over a DIY built polymer pack in my pocket for sure. Solder a 5v USB regulator, and USB cable, and you would be good to go.

 

[Bvillebob]

You know these are available cheap on the market pre-made, and there's a significant risk of blowing up your phone with a homebrew one, right? I'd do the math and see if it really makes sense to homebrew one (and I'm a huge proponent of building myself when it makes sense).