One Solar Panel to Charge 2 12v Batteries

[BlackOak]

Quick (maybe dumb) question. I have one 100 watt 5.6A solar panel. I want to trickle charge my 2 12v parallel connected battery bank. Do I need to run an additional cable from the battery connected to the solar panel to the other battery or since they are already parallel connected it not necessary? Will they basically balance out as they are?

If I add a 3rd battery in parallel, will I need to change anything?

[delmarrey]

If the batteries are the same rating and the same age and have been in parallel since the beginning, the one wire should be fine. If you start adding more batteries then problems will occur.

[noelex 77]

No you don't need an additional cable.
Ideally you will have the + wire leaving from the first battery to your switch panel and the negative wire leading from the last battery to your switch panel. You would then connect the solar panel the same way.

However lots of boats are wired so that the outgoing positive and negative wires come from the same battery. If yours is wired like this I would connect the solar panel in the same way. At the low charge and discharge currents your boat will experience it does not make much difference.

You will need a fuse close to the battery and should also have a controller (or regulator) between the panels and the battery

[djmarchand]

You definitely will need a controller. A 100 watt panel will boil your batteries dry if there is no on going load connected.

David