Now I'm using Bliss Pop some weeks ago. This is a great ROM, but one problem is the USB charging. If i use the radio in my car to charge the phone, its just slow down the discharge. So no up charging.
If I flash the agni kernel, to let me charging rates changeable, the phone is randomly freeze, or not wake up and screen is leave blank.
But this rom is the best for me, just this charging problems make me nervous.
I don't know how much you know about electronics, so I start explaining it the easier way.
I still use the i9305 (not with Bliss ROM, but Resurrection Remix, also a CM based ROM) and stock kernel and I also can charge it via my car, which has built in USB ports. The main problem with the built in USB ports is, they deliver only the current, a computer USB port can deliver and as it's USB 2.0, I get 500 mA theoretically, but actually I have about 400-450 mA (measured with an USB current and voltage "multimeter").
If I charge my device via those built in USB ports, while its screen is on for navigation or so, my device is discharging like yours. It discharges even faster, when I would activate Bluetooth, WiFi or mobile data and high screen brightness... so I bought a 12 V car USB adapter which offers two USB outlets, one 1,2 A and a second 2,4 A USB port. Even if I use to charge with the smaller 1,2 A (actually the device drops it to 1,0 A), my device is charging. The other fast charging port negotiates 1,5 A with the smartphone, so definitely not charging twice as fast, but also not getting twice as hot as well.
Please check the incoming current of your phone while charging at the radio USB port with the well known app
Ampere. It's not 100% accurate, but may show you the reason why your device is discharging. Test some sceneries, using the app with low and high screen brightness, with activated WiFi/mobile data/GPS etc. and with all those things shut off. If you try it with a 12 V car USB adapter with at least 1 A charging current, you definitely should get a charging state, even not fast though.
Please report back, so we can follow this issue, thanks.