24v panel charging 2x 12v battery while maintaining 12v operation?

[dannieboiz]

My boat has 2x batteries that are in parallel using a switch allow one or both.

I have a 24v panel that I'd like to use to charge the batteries when not in used. If I connect the batteries in series for 24v to the panels, does it affect the boat's 12v circuits if I forget to disconnect the panels before switching it on?

[Mike90250]

I would use a simple charge controller for 12V, and leave the batteries as is.

What is the wattage of the panel, and what is the Vmp spec of the panel ?

[dannieboiz]

Its 20w believe the vmp between 35-40v.

I already have the panels trying to use what I already have on hand.

[Mike90250]

simply connecting the panels to the battery will give you about 6 watts because of the voltage mismatch.

But, it's pretty odd to have a 20W panel in the 35V range. If you bought a MPPT controller in the $80 range, you might get the full wattage from the panel. So knowing the voltage determines the course you take.