Should I connect solar panels in series or parallel for my charger?
(In this case) you're better off putting them in parallel - your batteries will not rise to 12V.

With the solar panels in series you will also have other issues.  Imagine that one of the panels does not receive sunlight - it would generate a low current and the other panel would generate a high current - I do not think that the low current panel will be happy with the high current of the other one.