Ask the Mechanic

Battery Swap: 2 x 6 to 2 x 12

(Getty Images, Photo Illustration by Barry Falkner)

READER: I have a 4020 John Deere tractor that came with two 6-volt batteries. I want to change it over like the newer tractors that use two 12-volt batteries. I don't want to fry anything, but I would like to know how to do this in a professional manner.

STEVE: Since your tractor came from the factory with two 6-volt batteries in series, making 12 volts, that tells me it is a 1969 or later model. Since you already have a 12-volt alternator, your swap to two 12-volt batteries in parallel is easy.

After you remove the 6-volt batteries, replace them with two 12-volt batteries of the identical size (like those used in series on the dreaded 24-volt system until 1969).

Next, remove your old cables. The best way to make the new cables you now need is to measure from one positive post to the other, and then take a measurement from that post and place a post connector there, leading from there to the starter solenoid that will need an "L" eye on it. Both positive posts are tied together. Do the same measurement for the negative posts, making both negative posts tied together.

Put an eye on the ground cable end and locate a good ground. You now have only two cables. Make the cables a little longer than you measured, because you will need some extra length to run them under the platform.


-- Write Steve Thompson at Ask The Mechanic, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or email, and be sure to include your phone number.


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