Default [Q] why cant i fast charge ?

Hi got a gen 1 nexus 7. using it for an in car dash install. all works fine, BUT it wont fast charge. using Timurs ROM. got an OTG Y cable. it says on the " USB HOST " option under settings that it is fast charging but the battery still drains even just playing music. I thought it may be the battery so i have replaced it with a brand new one, charged it for a good 18 hours and still it drains pretty fast. just installed a CPU controller so that may save a bit of power use.... any ideas ?

thanks