Hey Cesar, Phil here from Tampa.
I fly the q500, my battery experience has been about the same, even as a new battery. The time on them is about two years, or till that get puffed or expanded.
FLT time was never morning than 10 min, now the two original ones are down to about 5-6 min. They are being retired.
In their place I found an after market battery supplier called Venom, through Hobbie Town.
Flight time way up and great quality. And less expensive.
Batteries will be an on going expense. Good luck.