The MPP LVX 6048 is one of the most popular all-in-one inverters on the market. Its very reasonably priced, has a large output and its split phase, meaning with a single inverter you can get 120 or 240.
The most common issue with LVX 6048 not charging a battery bank is that the customer does not have a high enough input voltage for the inverter. The LVX 6048 is a high PV input voltage unit, meaning that if the voltage going into the unit is less than 120V, it wont even detect the panels.
In order to increase the voltage of your solar panels, you need to connect them in series. Here is a video showing how.
So if you are not registering a charge from your MPP LVX 6048, make sure your input voltage from your solar panel array is at least 120V.