Bladderscan BVI 3000 Battery replacement box

The Verathon Bladderscan BVI 3000 is using 6 cells NiMh 7.2V battery. It is expensive, hard to find, expensive to renew and moreover uses a proprietary charger which is brittle and often missing, super expensive on the second hand market.

I saw listing on ebay for a used one with the battery swapped to lithium ion. I decided to make it myself. The free space isn't as big as I expected inside so I decided to make a battery pack which would protrude a bit.

I used 2 18650 (with battery protection integrated in them for shortage, overcharge, overdischarge), a battery holder, a battery charge display (model JX-4615-A3 ) and a USB C charger with balanced charging (model LX-LISC-V1 ).
I used multiwire cable to make the contacts. It's the wacky part, avoid shortage at this point! If you have better pads use it instead. 

No glue needed everything is pressure fit.