Wireless Keyboard 1-2 day battery life!
Since upgrading to OS X 10.11.4, the battery life on Wireless Keyboard (older model, not the new Magic Keyboard) dropped from about 3 to 4 weeks to 1 to 2 days! I am using Apple's rechargeable batteries and the same set of batteries hasn't affected Magic Trackpad (also older model).
And FYI, I only use the keyboard for about 8-12 hours.
OS X El Capitan (10.11.4)