I am adding a solar panel (100W Renogy mono) in an attempt to keep my AGM batteries happier than they have been. Just got off the phone with Ctek tech support re using a D250SA (new model) as my controller for a three-battery system (one starter and two house). The question of the moment is whether the D250 (or any controller) will actually allow current into the batteries under extreme heat conditions. Most controller specs say they have an operating range up to about 134F (the Ctek is 122F), and Ctek tells me that their unit will reduce output voltage as temps rise. Waiting for more info about whether extreme temps will shut the unit down completely or just slow it to a trickle. Ctek guy thinks it may shut down completely, but he is researching that issue. My truck often sees ambients between 110 and 120F, sometimes higher, and when the truck is parked on hot asphalt or hot sand, things really cook (cab temps above 180F while parked). But that is exactly when I need the solar panel to supply current to the house batteries running the fridge. So for those of you with solar in extremely hot climes, what have you seen in terms of actual charging when things get that hot? Thanks.