Maximum battery charge current by technology
is there a general rule for the maximum charge current (as a function of the battery capacity) for each of the mainstream battery technologies (NiCd, NiMH, Li-ion, Li-Polymer, lead-acid), for normal and fast charging?


I don't think so. It depends on a number of factors besides the chemistry, including:


what charge algorithm is being used
voltage accuracy of the charger (to prevent overvoltage on each cell)
temperature sensing ability (faster charge = potential to overheat individual cells)
# of cells in series (more cells in series = harder to keep cells balanced and charged safely)
manufacturer tradeoffs


This last point is important: maximum charge current is very highly dependent on how the manufacturer has made tradeoffs for energy density vs. power density vs. cycle life. Battery manufacturers such as Sanyo and Panasonic will often sell several different types of batteries, some with high power density, some with high energy density.

As a general rule of thumb, C/10-C/5 is probably safe for most chemistries without taking any precautions. Beyond that, you have to manage the temperature and voltage of the cells carefully in order to implement fast charging in the 1C / 2C / 5C / 10C range. 10C is iffy and I'd be surprised to see any battery of any type that could be charged at higher currents without sacrificing cycle life and safety.