>>472936No, it was definitely a factor of the solar cells.
Set it up in my windshield when we left, rode for ~8 hours, came back and it still wasn't charged. It was in full sunlight for at least 3 of those hours.
3-6 hours "dependent on sunlight" should be enough to charge it.
Maybe some day I'll meter it. Think I've got a couple of those size ends around here somewhere.