new to the brushless scene, need advice

[ridinbikes247]

i have a truggy with a feigao 8XL motor and a mamba max ESC...right now im running one 4200 sub C Nimh batterys ..i get about 5-10 minutes runtime an its not as fast as my old nitro truck...if i bought a y harness and ran 2(two) 4200 packs would i get more power ? or if i ran the wires different like series or parrell...also i dont want to hurt the ESC...i see it says 6-12 cells but it dosnt say how much volts it can handle...i disabled the BEC and i run a receiver pack