G'day Grant,

Your assumption is the right one in this case.  The display will show you the state of charge as a percentage, along with the charging status. 
If you want to keep ontop of your solar panels output, you could pick up an inline volt/amp meter which will give you this information without interfering with the charge.
We dont currently stock these, but you should be able to pick one up relatively cheaply from Jaycar or similar. They'll just have Anderson plugs each side.

Hope that helps.

G'day Phillip,

Assuming you don't have your lithium battery inside a box with a built-in charge regulator, I'd say go the 200W without a doubt. Heading into the winter months with less than ideal conditions, you'll maximise your chances with the larger panels - larger is better year round.

G'day Chris,

The 40Ah Companion is best paired with a 100-120W solar panel.  If you use a panel larger than this it will cut out above 5A or so, and reduce the overall efficiency and effectiveness of charging with solar.  As the panel is a larger capacity than the inbuit MPPT on the Rover, it may reduce the overall life of the unit.

G'day Michael,

No problems!  Just triple check the specs of the panels line up with the input specs of your batteries BMS.

G'day Andre,

The manual from the PLB 40 states that this unit can be charged with solar, but WITHOUT a solar controller, and the solar panel output requirements have to be between 8 – 25 V DC and a maximum charging current of 10A.
The 150W Crocskin panels can absolutely be used, but you'll need to bypass the controller and plug straight into the PLB40.