John I am adding 8 more batteries to my existing 8 that will be 2 years old by the time I get the second set of solar panels installed. I will have 2,400 watts of solar feeding 16 batteries. Looking to add a small wind generator that can get me 100 watts in 20mph winds as a secondary system to float the batteries but that will have to wait for more cash flow. Unless someone has a used 12 foot mini windmill they want to get rid of...
MaryAlana, I have strong doubts that a 100 watt mill will produce enough energy to float even eight 2200XC's, much less 16 of them.
You cannot parallel Trojan L-16's with your 2200XC's. US Battery has pretty specific recs for charging with a two-stage charger that does not match Trojan's recs
You can parallel eight more 2200XC's with no problem, with a few caveats. As I'm sure you're aware, US Battery uses a high-specific gravity electrolyte in the XC (Xtra Capacity) batteries and they will hit 1.300 SG with over-charging, which is not good. 1.285 is where they should be cut off or they will have actually less capacity being over-charged. With strings of different age I'd install a battery monitor like a Trimetric on each string as a monitoring tool to make sure that the strings of different age are exiting absorb at the right amps. The older ones that have been cycled will take more amp-hours than the new ones during absorb. This will cause the new ones to be over-charged and reduce their capacity and shorten their life.
Any other type of battery you can parallel just about anything with anything. But the US Battery XC-series are susceptible to damage if continually over-charged (note their 3%C absorb amp exit vs the industry "standard" 2% C exit current).
Call their tech support if you have any questions. I have talked to them on L-16HCXC batteries for our yacht a couple of times and they have excellent tech support there - absolutely the best tech support I have ever talked to at any battery company.