waveshare game hat with retropie and lo voltage/lo battery issues

[nogolem]

First I wanted to give the community a "warm thank you" for the job done around retropie those past years.
My Taito egret is so happy with it's raspberry inside :-)
a small Sony CRT TV runs it's old school games thanks to Retropie in my office...
The flat telly, even If It is in 16:9 has it's own flavor... games running in 4:3 with shaders and of course a copy of kodi, that I've been following since day One on the first Xbox.
I'm 51, my first computer was british lo end single board computer (Sinclair zx81) It was all I could afford in 1982, and I learned bits of BASIC.
I must say, I was quite happy with the arrival of an educational single board computer like the pie project.
Kodi, retrogaming and octoprint server for my 3D printer.

a couple of monthes ago, I came across the waveshare game hat over Ebay...
320/480 IPS screen ... I could NOT refrain for long before my right finger clicked "buy now" 😂😂😂
€36 with shipping to Paris, France !!
I have been using this hat for a little while with retropie and enjoyed a lot playing with it. after having changed it's screen ratio to 4:3 (black bands right and left side)...
I have issues with it's battery : It is an "MX JOE" 18650 battery, mainly used in Ecigs... NOT so good ..(rewraped they say)
this battery is advertised at 3000mah with a max instant current draw of 35 Amps.
I do NOT think It is true though, since I have not a long Time to play before I see the small bolt upright.
I think I am going to swap for a Sony VTC6 battery that seems to be a little better after reading tests on ECIGS forums...
this hat only uses 1 Slot for a 18650, and I was wondering If I could put a 2 batteries slot (in paralel) to get a better autonomy...
I admit I do NOT know anything about electronics and I was wondering If this could fry either the hat or the pie...
Does anyone have an advice about that ?
I know It is retropie forum and It Is NOT related to hardware. But maybe someone in this huge community has the answer....
voilà !
Please pardon my bad English...
good day everyone !
merci !