If not watching the state of the battery continuously is a must, I don’t think a separate app is necessary.
I just use the adb command
adb shell dumpsys battery
to check on the real current mah and percentage charged and I know exactly how far the battery has degraded so far. I own my device now for a week and just checked. It was 2991 mah on 64 percent which would give almost exactly 4700 mah on 100% charge. So I know my device had 100 % capacitiy out of the box.
Btw. I charge very often in between and just stay between 25 and 80 % (read Battery University site for details).
