I find it very funny that my anecdote on radio shack employees seems to have become the default example

Generally speaking, the theoretical time to completely charge a lithium ion battery from empty to full is 1 hour, assuming a maximum safe charge rate of 1C. Note that some of the newer cells and chemistries (such as lithium iron phosphate) can be charged at higher rates, up to 5C or more in some cases.

Anyway, the actual time is always a bit more than that because of efficiency losses in both the charger and the cell itself, ie the internal resistance dissipates some of the energy as heat. In practice, 90 minutes seems to be pretty much spot on for a 1C charge from a modern lithium charger. Some are a little quicker, but not much.

If the battery is not fully discharged, you'd think it would take proportionally less time, but it doesn't affect it as much as you might think. The charging process for lithium cells is constant current for about half the total capacity, which is quite fast, then constant voltage for the rest. This can end up being something like 60-70% or so of the total time. So if the battery is half charged, it can still take nearly an hour to fully charge it from that point.

One other thing, a new lithium battery may not reach it's full capacity for several charge-discharge cycles. It won't take any longer to charge, but it will last longer in the device until it reaches it's peak. It can be very noticeable in very high current applications, like for example electric model aircraft I'm still impressed I can pull 40 amps at 20 odd volts from a battery the size of a pack of cigarettes for ten minutes, and have the thing only just warm enough to be sure that it's been used!

There you go, more waffle on the subject of lithium cells than you ever wanted!

pca