AVR354: Using the Deep Under-Voltage Recovery Mode (DUVR) [PDF!]
DUVR mode represents the intelligent pre-charge mode for Atmel’s smart battery microcontrollers ATmega16HVA, ATmega8HVA, ATmega8HVD and ATmega4HVD. It is intended for controlled charging of cells even when the cell voltage is below the minimum operating voltage of the chip. The charging is done without using a precharge FET or current limiting resistor, and assumes that the charger is currentlimited
during the pre-charge phase. ATmega16HVA is used as an example in this application note, but unless otherwise noted one can assume that any of the devices can be used.
Have you ever used these ATmega HV chips? Is there a good overview somewhere of their features?