Arduino shed/outdoor monitor, batteries and solar panels

A brief update, I put in place my shed/outdoor monitoring system last weekend, installed the solar panel and monitors, and have so far had to change the batteries already, so at the moment it looks like they are only lasting 3-4 days maximum.

Upon investigating my 9v solar panel is giving out 2-3 volts, which is pretty useless. I'm trying to charge my 4 AA batteries (6 volts).

So my next plan of action is to take the solar panel back down and work out why it's only producing this very low voltage, I'm now wondering if the connections on the rear split the panel into two and I'm only connecting to one half (even so doubling 3 volts isn't near the 9v I was expecting), so a bit more investigation is needed.

(Yes I removed the plastic film cover! But it is inside a plastic box for protection, but even so I'd not expect the voltage drop to be that dramatic)

Graphs were being produced before the power failure though as you can see below:

(note the flat line towards the end is where the batteries died and I'd not written a failsafe into my graphing to 0/ignore results)