Most LiPo cells have + and - markings below tabs. Follow instructions i posted, and you should be fine. Your phone will only read one BMS (charging board), so you don’t want two sending mixed information to your phone.
In parellel, but only if two batteries are within very few mV of each other. They MUST be same mAH, or you will kill lower rated battery. First cut thin plastic or fireproof cardboard spacer, and place it between cells. Tape alined cells. Desolder top charging board from battery. Remove black plastic from top cell. Solder tabs + to +, then - to -. Nip lower black plastic, so tabs can fit under single charging board. Cover top battery tabs with tape or hot glue. Install pack same as you would single battery. Plug in phone charger. Fully charge battery pack, and enjoy. You now have a 1S2P 3.7 LiPo battery.
- Александр Борисович Мельников