I think from what I've read thats about right and its about where mine sits. Charging a battery completely and discharging it completely shortens its life. Therefore the hybrid system keeps the charge on ours between something like 50-70%. I think if the little battery gets to the top you are at about 70% and the system will stop trying to charge the battery. If its at the bottom its at 50% and the system will start the engine to make sure it stays about 50% (even if stopped). in the middle is good.

Thats probably oversimplfied but from what I've read here and my experience thats how it seems to behave.