Mark, I charge all of my LiCo and LiFe Li-Ion cells at 0.5C (and my NiCd and NiMh's too
). It's easy to remember, and yes, figuring out the charge rate is as simple as dividing the mAh rating of the cell by 2 (for 0.5C). For a 750mAh rated cell, you can go either 300mA, or 400mA, there's not that much difference. If charging the same cell at 1C, go no higher than 700mA. I say this, as most hobby charger's (but not all) charge rates are in increments of 100mA.
As I said before any LiCo cell in a size smaller than an 18650
can be charged at 1C. When you charge cells at 0.5C though, it really doesn't take twice as long, as you might think. I've never actually timed the difference, but would guess that it takes only about 20-25% longer to charge at 0.5C vs. 1C and as I said, it's easier on your cells, they will last longer.
Another advantage to charging at some rate less than maximum, is that it allows a safety margin, allowing for cells whose capacity is highly overrated. This isn't such a problem with AW, Samsung, Panasonic, or other name brand cells, but applies to most others.
As far as a minimum charge rate for Li-Ion cells, I don't think it's good to charge them at too slow a rate, as with older well used cells, you may run into problems with the charge rate approaching the self discharge rate of the cell. My personal preference is to charge cells at a minimum of 0.1C. You could probably go lower, but there really wouldn't be any advantage to it.
If you want to charge up cells in a hurry, the best method is to use the "Fast charge" feature of a hobby charger. This actually charges just the same as a regular charge, but stops the charge sooner at 0.2C of the original charge rate, instead of 0.1C, thus shaving off some time. The only drawback, is your cells will only be ~85% charged.
Dave
