Battery gauge never gets past half full

I just bought a 2001 insight, with 59,000 miles on it. I am trying to find out if the battery is charging properly, or do I have a potential problem. The charge and assist seem to be working as they should but the charge of the IMA batteries, in the week I have driven it, have not gone past the half way point on the gauge.My commute is over 70 miles round trip, almost all highway, and the battery will charge, just not past half way.Is this normal 0r should the IMA batteries take more of a charge than this. I have more questions, but I'll stop and see what answers I get to this.