So I got a BT mighty mouse for Christmas, and the batteries just dies like 4 days ago. So that was like 2 months, and 1 week of use on one set of batteries which is fine. I replaced the batteries on the 7th, and they are already down to 78%. At this rate they will be drained in 16 more days. The new batteries are just standard Energizer MAX alkaline batteries. Are the Energizer Lithium batteries that it came with that much better that it lasted almost 2.5 months, or is something else going on?