I came across this news brief on US patent for battery monitoring that may be better suited for portable devices:
"O2Micro® International Limited (NASDAQ:OIIM) was issued 12 claims under United States patent number 7,936,151 for its Battery State Monitoring circuitry; a continuation of the invention issued July 2010 under United States patent number 7,683,577.
This patented circuitry provides a "near-zero" current wake-up circuit for monitoring battery packs, during the stand-by-state. In conventional designs, battery state monitoring circuitry consumes excessive power in the stand-by-state, which adversely affects battery performance."
LEAF SL + QC
Received: April 19, 1 year after reservation