4 Batteries connection schematic

That's the easy part. Now you have to know which trailer wires go where on the batteries.

Thank you for all the responces. The diagram is great. Already saved for future references.

What KD4UPL said.
Also, they will last longer if you take efforts to wire them in a balanced manner as on the diagram below.


Or, the 2nd best, an almost balanced wiring - diagram below:


And, lastly, how you should not connect them - diagram below. It is still "correct" but terribly imbalanced:


For those who are interested why, here it is: http://www.smartgauge.co.uk/batt_con.html

Then hook all the positives together and all the negatives together.

We have four 12 volt batteries.

It's critical to know whether you have 4 - 12 volt batteries, or 4 - 6 volt batteries.