I did a teardown of the RG353P and found out that the battery does not make contact with the CPU as was assumed. I was able to put some copper heatsinks as
Ciszean 1x 3000mAh B0PGE100 / BOPGE100 Replacement Battery For HTC One M9 M9+ M9W One M9 Plus M9pt Hima Ultra 0PJA10 0PJA13 - AliExpress