AGM battery capacity interpolation

Torleif Registered Users Posts: 7
First of all - a great forum!
I will install a battery monitor (Victron - BMV600) on my solar system. I have a couple of AGM batteries that are rated 200Ah(10h) and 290(100h). I need the 20h capacity for the monitor. The batteries are branded by a retailer here in Norway and it is imposible to get relevant information from them. Hence, I need to interpolate the capacity. Searching the internet it is clear that the discharge curve is not linear, and I see from looking at a number of AGM battery specs that the capacity ratio (20h/100h) varies considerably. Are there any suggestions out there?