Several connected batteries (a battery bank) is considered one large battery for this type of question. The entire bank is charged as one unit. A much more complicated answer is possible if looking at Lithium cells.
A good 3-4 stage RV style charger/converter is worth the money. Something like this
. Be sure to select one that matches your battery bank voltage, chemistry, etc. The output rating (45 amp on that one) is related to how much power you require when in 'converter' mode (supplying DC power to the house) and the appropriate rate of charge for your batteries. There is an ideal (depending on battery chemistry, bank capacity, state of charge, etc.) but that involves a bit more information/design.