your taking advantage of the quick charge feature of lithium ion batteries.

Due to their nature, they are able to accept high discharge and charge rates, but in order to prevent heat buildup and safety issues, the fast charge only works up to 80%, the last 20% the voltage drops dramatically and the battery is filled much slower.

if i have to assume 1 hour to 80% and then 2 more hours to 100%, but lithium ion batteries don't like to be discharged like TheGeneral was saying, however, i'm sure even if the unit did die out (not able to turn on) the battery TRUE state of charge should be around 30%, because anything below that and the cells are damaged. Your capacity will drop dramatically

however, the new age of lithium batteries such as phosphate solves this safety, charging times, life and hopefully one day cost. Bank on the electric cars to evolve that segment.