This 20A charger comes standard with three outputs which can be fed to three different banks. The output is distributed by demand not divided equally as some chargers are. So if a start battery was at 99% state of charge and your house bank was at 60% state of charge the house bank would likely be seeing the vast majority of the charging current 18-19A or so and the starter would be seeing 1-2A or less.
For owners who have a charge distribution system in place, such as an Echo Charger, Duo Charger, VSR (voltage sensitive combining relay), or in the US often referred to as an ACR (Automatic Combining Relay), the outputs can be "jumped" together as shown to create a simple "single output" charger.
Technically with this charger you don't need to "jump" the unused outputs if using it as a single output charger. The US distributor feels, and I agree, that it is a wise idea to equally load the output FET's so I chose to jumper than to even load the outputs. The two red jumpers are jumping output 1, 2 & 3 to load all the output FET's equally. This essentially makes the charger a single output 20A charger rather than a three output 20A charger. All current in this installation will feed to the house bank and the starting bank will be charged via a Blue Sea Systems ACR relay. You would do the same with an Echo or Duo Charger.
This particular boat has an ACR / Automatic Combining Relay so the charger is being used as a single output. Keep in mind that nearly all chargers, with the exception of some very expensive ones, still only have ONE output setting, in terms of charge profile, so dividing it up is not really necessary unless you don't have an ACR, Echo Charger or Duo Charger type of battery bank charge distribution.
Also note the location of the green fuse. This is the charger output fuse and it well located and easy to change if necessary.
The two heat shrink ring terminals are just illustrating where you can connect the neg and positive battery leads to.
It should be noted that on 30A and larger Sterling Pro-Charge Ultra chargers they use large studs as opposed to a small terminal strip for the DC output. I really wish the 20A model had these studs too but it does not. For that reason alone I would suggest considering the 30A or larger model if you can.