PolyRC has a lot of grades of cells as do most companies

It may be an older gen pack pack - which ages them and increases internal resistance

Also cell heat isnt bad as long as they come about in the 50 celcius range - preheating to 45+celcius reduces the internal reistance and delivers a definite boost to voltage under load.

Finally continuous/peak ratings are arbitrary. nothing runs continuous amps and only LMR gliders nd drag racing run real peak amp loads.

Altho I use Thunder Power in all my marine racing I use the continuous rating as a peak rating. I only hit it when i enter a turn at full speed. i run the same course every time and take out 2300-2600mah from a 5000mah pack in 60-80 seconds the packs ciome ina t 45-50 degrees celcius