From Home Power:
The maximum recommended rate is C/5 (a charge rate in amps of one-fifth the overall battery capacity in amp-hours), but only when the cells are between 10 and 85 percent state of charge (SOC). After the cells reach 85 percent SOC, then a C/10 is the maximum. After cells reach 95 percent SOC, between C/20 and C/15 is recommended. Having said this, I rarely charge faster than a C/10.
The reason for the maximums is heat. Higher amperage means more heat, particularly when the cells are getting fully recharged. Thermal cycling wears the plates and sloughs off material.
Finally, itís always a good idea to get charging specifications from the manufacturer of the particular model of battery youíre running. Battery specific charge rates, and bulk, absorption, float and equalization set-points and times will all lead to better battery longevity.
Richard Perez ē Home Power
I have never seen a respected Battery "expert" that didn't refer you back to the MFR - Why? - because they've already done the math on each of their Batts - Below is a link to the math - HTHhttp://xtronics.com/reference/batterap.htm