Fuzzbean noted that Amazon is mixing reviews for the 5 watt version (which this review is about) and a less powerful version (2.5 watts) so pay attention to mentions of suction cups - they are apparently included with the 2.5W as there are no suction cups included with the 5W edition.  Not that I have anything against suction cups, you understand.I'm tardy in posting this Vine review because I found this difficult to seriously test in my environment.  I have no rarely-used vehicles.  The battery I need to maintain is really two batteries connected together in parallel to supply an inverter for emergency use during a power outage.  Each of the two is a 12V 110Ah AGM battery (relatively robust batteries).  I didn't expect to be able to tell that this device was doing a lot for them as they take a while to drain appreciably under load and my guess is that a low-volt/low-amp trickle charge would take days to recharge them if it ever did.So I just hooked up a borrowed multimeter and started taking measurements.  Even with a pretty good coating of pine pollen (it's that time of year in NC) and full cloud cover I was consistently seeing 6+ volts  When I wiped the panel clean and the sky cleared, I tried again and consistently saw readings of 7 - 8 volts even though the panel was not in direct sun.  Due to my own ignorance I was unable to get a reliable milliamp reading but I'm hoping that since the voltage output exceeds promises, the milliamps at least meet them.  This 5W version promises 410 milliamps vs. the 2.5W version's 180 milliamps.One thing that bothered me a little was a "helpful tip" in the accompanying instructions: "For extra waterproofing and to extend the life of the panel, cone bead around the edges of the inside frame."  I guess I should be handier, but "cone bead" implies to me that I need to go buy some kind of caulk (last time I was at Wally World there were a zillion kinds of caulk and you can count on me to always choose the wrong one) and seal the thing up.  If this is a good thing to do, why not just do it before it leaves the factory?  Anything I put caulk on ends up looking like a pastry item decorated by the Three Stooges so maybe I'm just overly sensitive.  And don't get me started on "cone bead" as a compound verb.I should confess that I own a NOCO Genius G7200 charger/maintainer that I'm very happy with, so I may have a bias toward their products (for the suspicious, the G7200 was not a Vine thing; I bought it with my own real money).  I was tempted to ding this solar panel a star for the "cone bead" thing but gave that star back because these people seem to offer good stuff at reasonable prices and this feels like a solid, well made item.  If you have use for this kind of thing, the current Amazon price of $35 seems very reasonable.