Battery Ah / Time *.25 = 1mA

Example: 65Ah / 504H (3 weeks) * .25 = 32mA

With a 65AH rated battery, it will go for 3 weeks at a 32mA draw and be at 1/4 capacity.

I am sure this is not 100% accurate, but this is how Volvo states it. Login to read more.