The battery indicator app in the first picture shown appears to be ours so I'd thought I'd respond. :-)
The ongoing notification shows because all ongoing notifications in Android currently must display a notification as shown, and because the app must always be in memory to work correctly. You do not need a custom rom to be sure the battery is not being drained too much.
Over a year ago I joined with Dmytro Shkil to publish both Battery Notifier (Big Text) and Battery Notifier Pro BT because his original program consumed less battery than any other app I had tried. Tested with SystemPanel with the display intentionally kept on, the free and paid versions of our program today still consume less than .01% CPU over 8 hours.
We have left out fancy graphs and other eyecandy to keep our app consuming as little battery as possible.