Auxillary battery charging in car?

[mjz]

I want to put a battery tender on my 2025 Wrangler JL Auxillary battery to keep charged while not using the Jeep for the next few weeks.
I read that posts N1 (+) and N2 (-) are used for this, but when I test the posts, I get zero volts. Has anyone put their AUX battery on a charger before?

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[AndySpill]

I want to put a battery tender on my 2025 Wrangler JL Auxillary battery to keep charged while not using the Jeep for the next few weeks.
I read that posts N1 (+) and N2 (-) are used for this, but when I test the posts, I get zero volts. Has anyone put their AUX battery on a charger before?

1) Two black factory cables will connect to the main battery's negative post. One of those cables has as its other end the body ground on the passenger's fender. Leave that cable connected. Disconnect the other cable at the negative post of the main battery and attach the negative end of your charger to it, keeping it away from vehicle body metal. (The distal end of that cable connects to the Auxiliary battery's negative post.)

2) Put the positive side of your charger on the positive terminal of the main battery. That's right, the main battery, even though you wish to charge the Auxiliary battery.

This will charge only the Auxiliary battery as its the only one with which the charger completes an electrical circuit: the positive post of the main battery being connected to the positive post of the Auxiliary battery.

All this said, I'd just put my charger on the positive and negative posts of the main battery and trickle charge both batteries: the factory parallel connection between the two when parked insuring that.

If you follow my prior steps though be sure to reconnect that cable before using the Jeep again.

 

[AndySpill]

I want to put a battery tender on my 2025 Wrangler JL Auxillary battery to keep charged while not using the Jeep for the next few weeks.
I read that posts N1 (+) and N2 (-) are used for this, but when I test the posts, I get zero volts. Has anyone put their AUX battery on a charger before?

By the way, as per the following linked diagram https://www.jlwranglerforums.com/fo...ry-consolidated-information.25377/post-602294, in dual AGM battery JLs like yours, N1 connects to the positive terminal of the ESS battery, and N2 to the positive terminal of the main battery.

Accordingly any meter that tests voltage, as I think you claim to have tried against these two points, would not be expected to measure voltage for essentially the same reason that putting such a voltage meter's two testing leads both on the positive (or negative for that matter) pole of a "AA" battery, or two "AA" battery's positive poles, even if those positive poles were connected by wire, as is the case in the JL.

 

[mjz]

By the way, as per the following linked diagram https://www.jlwranglerforums.com/fo...ry-consolidated-information.25377/post-602294, in dual AGM battery JLs like yours, N1 connects to the positive terminal of the ESS battery, and N2 to the positive terminal of the main battery.

Accordingly any meter that tests voltage, as I think you claim to have tried against these two points, would not be expected to measure voltage for essentially the same reason that putting such a voltage meter's two testing leads both on the positive (or negative for that matter) pole of a "AA" battery, or two "AA" battery's positive poles, even if those positive poles were connected by wire, as is the case in the JL.

Perfect! Thank you!
(I did notice checking N1 against N2 - zero volt difference. Your diagram perfectly illustrates why.
Interestingly, when I put a battery tender across the main battery terminals, N1 does show the charging voltage (meaning the aux battery is getting charged at the same time))

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