Just another <span class="highlight">solar</span> setup inquiry sorry about this but brain has frozen

I'm a little confused by the [4.8A] and the charge rate 4.2A@12.7V can you elaborate?

What is the voltage being applied to the battery, if the charge rate amps is less than the panels can supply I would expect to see around 14.4V at the battery terminals?

You have a couple of issues.

#1..solar pannels do not produce their rated output unless they are in direct sunlight, correcty aligned, in the middle of the day, at the height of summer and in a high radiation location.

In a low radiation location like tasmania or soutyhern victoria in winter you may find pannels maxing out at 20% rated and then only for a couple of hours in the middle of the day.

#2..you have two mismatched solar pannels on unmentioned length of cables.....the pannels will not be doing an equal share.

Because the pannels are mismatched, the regulator may have difficulty tracking a maximum power point......the whole point of maximum power point tracking is presenting the optimum load to the pannel and delivering the optimum charge to the battery...I direct relationship with a single pannel or a matched array and a dorect relationship with a single battery or matched bank....is required for optimum tracking of the maximum power point.

#3 it has been proven that cable that is too light or too long can drasticly reduce performance.

#4 just because a charging system..any charging system is capable of delivering current, it does not mean that a battery will accept it.....particularly if the battery has some age or has developed charge resistance.

I would not go lashing out on a new regulator just yet...it may make no difference.

There are a number of issues for you to work thru.

cheers

The vehicle panel will not be square ON tot he rays of the sun so it's voltage may rise but the intensity oof the energy delivery just won't be there. It's output will be vastly reduced if angled to the sun as it will be most of it's life unless around lunch time.
The folder panel will be more suitably aligned though.

The Tug system is shorter wiring and the folder longer wiring.

While both are working around midday, and aimed as well as possible, have you measured the voltage drop at the panel end to the reg end of each conductor in the twin core wire cable? ie, The voltage drop from one end of the POS cable to the other end of that wire, should be the same voltage drop as the negative line returning the current flow to the panel.

Same for the tug panel and it's wiring.
Expect the folder to have a more voltage drop if the same voltages are measured at both panel junction boxes if same sized cable is used. ie longer cable run.

With both panel systems to the reg, if the cable size is causing significant voltage drop it will reduce the charge rate possible with just a small VD happening.

The panels are merely charge pumps and anything not at the optimum will reduce the pump "Speed"/"Intensity".
So, all connections and wiring has to be assessed to find the issue.

If you have a larger battery bank, the afternoon float time could be used to continue charging that battery AH capacity as well and in the morning the battery system will be at a higher voltage level with the same night time usage.