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I don't know anything about the Sunsaver Duo, but so long as they do not share a common negative between the two sides, then it should be possible to charge each individual battery while they are also connected in series.� But I can't stress this enough... the two sides must be isolated, otherwise there will be a voltage across the shared part and it will probably blow out your charger.� I did this for a short time -- I have 6 4v batteries in a 24v bank, and I used a dual 12v charger on each half.� It worked OK, but I upgraded to a 24v charger when I had the chance.
I'm not sure the 12-48v DC-DC converter suggested will be useful since the amps delivered will be paltry.� Although a 92AH battery bank is pretty small, you want to push at least 10A to it.� Most likely, your Sunsaver only puts out 10A @12VDC on each side, which is only 2.5A @ 48VDC.� If you sent this @12VDC to each battery individually, it would be sufficient, but just one leg of one charger to the whole bank @48VDC wouldn't cut it.�
Your best bet is a 48v capable charge controller such as the Outback Flexmax 60:
http://www.altestore.com/store/Charge-Controllers/Solar-Charge-Controllers/MPPT-Solar-Charge-Controllers/Outback-Solar-Charge-Controllers-MPPT/Outback-Flexmax-60-Solar-Charge-Controller/p6875/Then you can connect your panels in series and your batteries in series and connect the leads of each to your charge controller and it'll just work.