Chosen Solution

I use my mi5 as a flight instrument. I want to get a bigger battery directly connected to the motherboard. Xiaomi do have bigger batteries but the connection cable isn’t in quite the right place I want to buy i.e. Mi max battery and buy an extension for the connection. There’s no back on the phone, size not important. I don’t even know what the connection is called. Cheers

Probably cheaper and easier to just buy a power brick and a USB extension

This is on my paragliding flight deck and unfortunately what happens is the cable breaks, the phone USB breaks or the batteries USB breaks. They’ve all happen to me before . I really need it connected at the rear of the phone with an extension or directly to the board. Thanks though