I had been running a 5s setup using a 2S 5000mah 25c/50c and 3S 5000mah 25c/50c. Both are Neuenergy batteries and same age. So far no problems at all.
Castle Neu 1520 on 6S LiPo Powered Gmaxx (Nitro Killer)
Predator with OS .21TM
Supermaxx with Mach .26
Revo with OS .18TZ
Kyosho ST-RR Conversion
Ofna CR with Tekin ESC/Motor (2)