RJCorazza wrote:

I looked into higher discharge rates, and found the law/effect mentioned :
Puekert's Law, which unfortunately requires knowing the 1 hour rate (as opposed to the ususal 20 hour rate). There is also a constant for various battery types, age, and condition. This constant seems to range from 1.2 to 1.32 for standard wet cell lead acid batteries. An adaptation of Puekert's Law apparently exists that is incorrect. The adapted formula that produces reasonable numbers is : T = C/(I/(C/R))n X (R/C).
Where:
T=time in hours
C=capacity of battery in AH
R=battery hour rating (20h rate, etc...)
I=discharge current
n=Puekert constant (exponent)

For the example under discussion the calculation yields an answer of 44 minutes to a 50% DOD. All said and done, it's really just an estimate...