Is there some way to charge a battery bank from the grid in HOMER?
Yes, you can charge the battery from the grid.
There are a number of control parameters under the advanced tab of the grid component. There are a number of settings that can be used to control the battery charging strategy according to grid price. For example, you can prohibit the grid from charging the battery above a certain $/kWh grid power price. There are a number of options that should be considered to control the grid and battery interaction.
If you are just trying to limit your peak grid demand, use the purchase and sales capacities under the advanced tab. This is appropriate if the capacity of the grid is limited and you need the battery to meet the load peaks.