Don't even think of charging a pack more then 700 ma with a 50 ma charger, it will never charge fully and you will crash.
Really? Gosh, I better tell my wal wart charger it's not up to the task! [X(]
Sarcasm aside, I've seen this assertion several times. The 10% figure is not a MINIMUM, it's a guideline MAXIMUM for safe slow-charging. Staying at, or below, 10% provides relatively fool proof charging. Going above 10% can be done, but requires closer monitoring or a charger that can detect peak and shut off or switch to a lower current. I've charged plenty of 2000+ mah batteries on the standard wall wart charger that puts out less than 100 mah. While this is not a particularly fast method, if given enough time they do reach full capacity.