[grumbel]

The AA lithium-ion rechargeable are internally 3.7V, just like any other lithium-ion battery. They have a buck converter build-in that regulates that down to a constant 1.5V. Which can be handy in the handful of applications that don't deal with the 1.2V that NiMH provide. This does in turn make battery indicators indeed completely useless for many of them, as there is no detectable drop in voltage from the outside of the battery.

However, there are newer ones take care of that and regulate the voltage down to 1.1V or so shortly before they run completely out of juice, so that the battery indicator can give a warning. Don't know how widespread that feature is yet, but it exists.