Yes, you need a fully charged battery to run the slides. When you plug in to shore power, it should trickle charge the battery. But it would be faster to actually put a charger on it, and let it charge overnight on 12V low setting. Normally, you should not need the generator to charge. We leave the shore power connected full time while sitting in the driveway at home, and it keeps the battery at full charge. Also, don't let a discharged battery stay in freezing temps - it can and will freeze and crack the case. Hope this helps.
2003 Ford F-350 V-10 Crew Cab 4WD Long Bed
2004 Jayco Designer Medallion 29 RLTS 5th wheel
Bill, Gayle, and Mindi (dachshund)
Retired at last !
Nothing is foolproof to a sufficiently talented fool.