Great Whit3

Guys I came across my brother in law's geyser. The cold pipe runs under the tubes to the outlet of how mine is plumbed. The hot pipe on mine is the outlet of his going back into his geyser. I will contact the plumber this week. What's your guys thoughts? 

It is purely due to the more than 2 times load. If you want to know if battery is still as new you need to charge to the same SOC and then rest the battery for a few hours and no load and then get a reading. 
Not easy to do with the LS at the moment and little sun and lots of rain if you are in the Northern part of SA. 

This appears to be an Axpert clone. With 75 V max PV voltage, it's possibly a PWM model (not MPPT).
Two 420 W panels in series is possibly too much voltage, especially if it really is a PWM model. Try wiring the panels in parallel instead of in series.
Edit: that's assuming that they are currently in series.
Does the PV icon come on at all?
As you press the up or down buttons, you should come to a page that shows the PV voltage. What does that read?

Yes you can use 0.9x2.4kWh from battery. Bear in mind that is full sunshine day. Some bad rainy days you can get as little as 10% production and quite a bit of 25% production. As you have grid more battery power will help even if charging from the grid. Bad news as you know this is expensive. 
Even 380W for 16hrs when PV production is low/zero needs quite a bit in storage. 6kWh.

Yes you can only put all 4 in parallel due to the 80V limitation.