Craig, On my Krogen 42 I have two standard PV panels connected to the same switch you have, but my switch controls only current FROM the panels to batteries, and not from the batteries to any loads. I keep my boat on a mooring in North Carolina. Normally the panels feed my Lithium 330 AH house/engine/generator start battery. I can switch the charge current to my backup generator start type 24 battery if it is needed but don’t want to parallel the lithium and wet cell battery because I don’t know what the consequences might be and there is no need to do it. I also have two type 8D wet cells to run the 24V bow thruster that are completely separate from the 12 volt system, but each can be charged one at at time by manually connecting alligator clips from the PV panels or using a small 24V charger through the inverter when on generator power. I don’t see why you couldn’t connect your PV panel to “both” on your switch though the charge rate for each battery would be less, but I prefer to use a separate switch for the PV so I can turn it off when the engine alternator is running. It may not be a problem for both sources to be simultaneously charging the lithium, but I prefer to use the PV when at anchor only and keep each charging source separated, whether it be alternator, PV, or generator. Perhaps someone on this list who is smarter than me could comment on this. As an aside I have been very pleased with the Lithium replacement for 4 golf cart sized batteries. It works just like your cell phone with about as little thought. Have had it for 3 years and nary a problem. Pricey to purchase (like a smartphone) but over the long haul I think worth it as the full 330 Ahr is useable with full output and you can see at a glance how many amp hours remain (I have been below 50% only twice as my PV panels provide about 80% of our daily power requirements while at anchor, and we use the generator only if we need air conditioning or a rare Li charge.) John Sams KK42 Liberty Call Lying on her mooring Edenton NC Sent from my iPad On Dec 7, 2019, at 10:30 AM, Craig Mudge via Trawlers-and-Trawlering <trawlers@lists.trawlering.com <mailto:trawlers@lists.trawlering.com> > wrote: Greetings listmates, I need some guidance wiring my new solar panel. I have a pair of 4D batteries on my boat. They are wired through a typical 1/2/Both/Off switch. I added a Renogy 100 watt panel with a smart controller this season. It’s currently connected to one of the batteries. Should I connect the charger output to both? Thanks in advance, Craig in Camden, Maine