Your question is unclear, you don't say what your existing battery bank voltage is.
Assuming you don't have a battery bank and are setting up from scratch, I would highly recommend avoiding a 12v battery bank. I went with 24v, others use 36v or 48v. If you go above 50vDC it no longer qualifies as "low voltage DC" and the NEC requirements become enforceable (in the US).
If you have a 24v bank, you can get 12v from it by using a DC voltage converter. I use a Samlex SDC-30 which is no longer available but they now offer a 60a continuous version in its place. The nice thing is that I'll still be getting my 12v (actually 13.74v) nice and solid until the batteries are discharged far too far, until the 24v bank is down to around 16v. It isn't something one wants to do, but it could come in handy during a blizzard or some other emergency situation. If I had a 12v bank and was running DC loads directly connected, the DC voltage would vary with battery discharge and my 12v appliances would be attempting to use 11.8v or whatever.
Keep in mind that if you have a 24v battery bank you'd (traditionally) want to be able to charge it to about 29-31v which you cannot do if your generation equipment is putting out exactly 24v.
Probably the largest drawback of a 12v bank is that you need very large cables because for the same power level a 12v bank will be supplying twice the amps as a 24v bank would.
If you have 24vDC and need to use it to charge a 12v battery bank you could probably use a Samlex SDC-60 to convert it to 13.74 volts which would be a reasonable (though not optimal) charging voltage for a 12v bank, if its 60amps continuous ouput is adequate for charging purposes. I'm sure they have other converters available if current above 60a is required, and I'd contact them and ask before purchasing.
Some solar controllers will accept various voltages and convert them downward as part of their charging process, but many state that they aren't intended for uses other than solar. Other, non-solar, charge controllers exist I believe.
If you need more help posting some more information would be helpful.