OK, I will jump into the fray here!!
The dealer is partially right. Lead acid batteries charge fast when they are significantly depleted. At 50% SOC they can charge at 0.2C (20% of the amp hour capacity). But as they charge up to 80% and beyond it drops off. Just guessing for illustration purposes, at 80% SOC they will charge at 0.1C and at 90% at 0.5%.
So unless you run your generator all day you will not get to 100% after starting at 50%, thus the dealer's statement.
Solar is the perfect "top off" charging system as long as you are not shaded. In the morning use your generator for a few hours to get to 80% or above, then let your solar top off the last 20% over the day.
A solar system rated at 0.1 * (C*12) should work well to fully charge up the batteries during the day as long as it isn't shaded.
David
__________________
|