Logitech Replacement Batteries

Logitech MX800 Mouse and Keyboard 

About a month ago I went to use my Logitech wireless keyboard and the light was blinking red when I tried to charge it. I found out that it meant the rechargeable batteries weren't good anymore. A few days ago, my mouse was dead all of a sudden and it too started to blink red when charging. So it was time to do research to figure out what were the appropriate batteries to get as a replacement. Boy, how rechargeables have changed. The two devices were purchased at the same time so it isn't too surprising the batteries failed pretty much at the same time.