Multiple Batteries

I have noticed on the new TMs that they come with two 12v deep cycle batteries. My TM is a 98 and was originally equipped with a single battery. I would think it would be easy to add a second 12v battery next to the existing one. My question is are the batteries connected in series? I am not very electrically inclined, but I would guess you could connect the positive from one battery to the negative of the other battery and then complete the circuit with the connections to the TM. We typically travel with our refrigerator on 12v power, so I would think the two 12v would give us additional time.

Any suggestions?

[Civil_War_Buff]

If you connect the batteries in series (+ to -) then you ADD the voltage. Which would mean 24V in this case. Connecting in parallel (+ to + & - to -) will ADD the Amps only and keep the batteries at 12V. Connect the plus to plus and neg to neg and you (as well and all of your 12V appliances) will be very happy.

Larry