My bluetooth keyboard reports low batteries even when they are fully charged, then disconnects.

I have a bluetooth keyboard that, until recently, worked like a charm. Now I continually get the low battery warning so I replace them with fully charged ones and after 4 or 5 days I get the warning again. I have tried several sets of batteries and still get the low warning and eventually get disconnected.

I am running Yosemite 10.10.3 on a Late 2009 27 inch iMac.

I will check my bluetooth mouse and it will read 98% battery level, so I will switch them with the keyboard (12%) and then I still get keyboard reading say 22% and my mouse now is 100%?

I have used my Fluke meter on the batteries and they will read 1.28 to 1.34 volts which is what a fully charged rechargable should read.

Anyone else have this issue?

Thanks.