Battery Longevity Mode

Hi,  I have been using a netgear nighthawk for over a year now with no issue.  Suddenly it is telling me it is in "Battery Longevity Mode"  

It does not charge past 65%,  it disconnects service after a few minutes of inactivity and I have to hit the power button to reconnect. 

I can find no mention of this mode anywhere online or in any manual.

Why is it doing this?  How do I disable it?   Is this a battery failure mode?

I rarely ever run this off the battery, it is usually plugged in.

Thanks