How to power CB radio without aux battery drain

[Mr Miami]

I'm not an expert either, but my understanding is it's not simply "adding power", it's providing a stable alternative for electronics/accessories. Not only does it power the components when the engine is off during Auto Stop/Start, it provides voltage stability when the engine cranks (due to the demand on the main battery from the starter) and/or other high demand/load scenarios.

Yes, I think we need one of our experts here to comment. I get everything you are saying but I still don't understand why a larger, stronger battery would not simplify the entire process. Additionally, as I understand it, both batteries should be changed at the same time even if one is still totally functional. At least that is what I have gleaned from some posts on other threads here.

It still seems strange to me why the second one is needed. It's not like Jeep can market or sell it as an "upgrade" or better standard equipment as in the case of providing the full sized spare tire instead of the donut thing that was used in the past (and maybe in some cars today?). What can Stellantis say, we have a second hidden battery that costs them more money and us more money that may be an additional maintenance expense without stating what it is doing better or improving?

Sorry if I am rambling, I get your point, but it still makes very little sense to me.

Sponsored

 

[Mr Miami]

This is exactly correct. It's not about how much amperage is available, it's about making sure your electronics don't reboot in the middle of the road when it starts back up from an ESS stop. That tiny moment when the starter engages after ESS is where that battery comes into play (other than the self-test, obviously). All other times, it's in parallel.

Think of it like a dinghy on a yacht, or a life ring. Always attached to the boat (main) and always floats with the boat except that brief moment you might need it, at which point it's momentarily separated.

That you. I was just responding to the other post before I read yours. I see what you are saying. It's not always parallel, which is what had me a bit confused.

Since you have a far greater understanding on this and I am in Electronics 101, does it need a battery of that size to do what you are stating? Isn't that, sort of, what a capacitor does? If not, if only for such a brief moment of use to protect the electronics, couldn't something the size of a pack of cigarettes attached in a more accessible place under the hood do the same thing?

 

[sharpsicle]

That you. I was just responding to the other post before I read yours. I see what you are saying. It's not always parallel, which is what had me a bit confused.

Since you have a far greater understanding on this and I am in Electronics 101, does it need a battery of that size to do what you are stating? Isn't that, sort of, what a capacitor does? If not, if only for such a brief moment of use to protect the electronics, couldn't something the size of a pack of cigarettes attached in a more accessible place under the hood do the same thing?

That's a good question, but I don't know what the designed requirements are for that system relative to expected load and voltage maintenance. That would be a internal Jeep tech document. Chances are that yes, something smaller could do the job, but then you build in a safety buffer in the battery capacity spec, and then use the closest mass-produced size up from that.

 

[SaiintNick]

How do I bypass the aux battery?

All I did was pulled the #42 fuse and disconnected the aux ground from battery. No problems in the last week since I did it.

 

[Mr Miami]

All I did was pulled the #42 fuse and disconnected the aux ground from battery. No problems in the last week since I did it.

I don't have the issue yet (hopefully not for years to come on my '24) but I like your simplicity of design.

 

[SaiintNick]

I don't have the issue yet (hopefully not for years to come on my '24) but I like your simplicity of design.

Yeah I had a service transmission message. Then never again. Then a month later I remote start the Jeep and it started and then shut off. Then pushed button and it started and then shut off again. Someone mentioned the aux battery. Called dealership and the advisor immediately said aux battery. It's still covered under warranty, but I didn't want to leave my Jeep and go through the hassle when its such a stupid design that will continue to fail.

 

[Gray Matter Jeep]

Any chance a "going dead" Aux Battery could cause the Center Instrument Cluster to go dark? About two months ago my Center Instrument Cluster (behind the steering wheel) went dark.

Now I am noticing the Auto Start Stop is not working. For example, my engine has not been shutting off when I'm at a stop light. My daily drive is only about 3 miles, yah 3 miles, and my errands around town are less that 20 minutes at a time... so I just figured the Aux Battery hasn't been getting charged by the alternator?

Fast forward to yesterday, when I drove my JT for 2 hours (nonstop on highway). I couldn't help but notice the Auto Start Stop is working again. Are these two symptoms connected?

Is my Center Instrument Cluster not working because the Aux Battery is going bad?

 

[Lo Tek]

So ... if the aux switches are involved, why not use one of the 10A circuits (1 Ignition, 1 Battery) in the passenger footwell? Which now makes me wonder of the 10A Battery circuit (if you want power when the ignition is off) has any sort of low voltage protection that would cause it to shut off before the battery was drained? The Midland MXT575, for instance, only draws 300ma (max) in standby, but if left connected for some time without starting it could be problematic.

 

[bd100]

There is a thread here or the JL forum which shows via oscilloscope that the aux battery is kept connected to the main battery essentially all the time, except for a fraction of a second when ESS restarts the engine. For that small amount of time, the starter is pulling lots of "inrush current", so they disconnect the aux battery during this fraction of a second to prevent the starter from dragging down the electronics, then reconnect it after that power surge has passed. To avoid aux battery problems, those who disconnect the aux battery also disable the ESS system so the engine stays running. If the engine were allowed to stop and restart with the electronics directly connected to the main battery, the electronics may be glitched.

Yes the Aux battery can cause all kinds of chaos. If it is weak then the electronics get a brown out. When troubles appear, replace or bypass the aux battery, but don't leave it be or it will drain the main as well. An early symptom of failure is if it never does engine start/stop at the traffic light, even if you've driven for a while. If it DOES start/stop at a traffic light, the batteries are probably OK for now.

It does take a decent drive time to recharge everything. If you do lots of small drives with ESS active, it drains the main battery for each engine start, and loses the chance to recharge during the stopped time. Double hit. If you turn off ESS then the starter doesn't drain the battery at each stop light, and the batteries can continue to charge instead. If you really like the MPG benefits of engine start stop, then put the vehicle on a charger every week or so.

If you like the aux battery and engine ESS system for MPG benefits, you may want to look at the Genesis battery systems. One of their systems relocates the aux battery above the fuse box for easy replacement. Another uses two mid-sized batteries in the big battery tray, one for main and one for aux. The advantage there is that they are the same size and may last longer, but they are a size which is harder to find locally.

For a CB, GMRS, etc, use the power port, or the wire harness mentioned above, or use the AUX switch leads if available. If the radio does not come with a power port adapter then it may draw too much power for the power port (10A or 15A?), and will require one of the high current AUX lines or a direct relayed battery connection instead The AUX wires are programmable for always on vs ignition on. The AUX switches will be disabled by the computer if the aux battery is weak and needs charging.

 

[Lo Tek]

The AUX wires are programmable for always on vs ignition on. The AUX switches will be disabled by the computer if the aux battery is weak and needs charging.

After all the ESS discussion this leads to my question - within the AUX switch wire bundle are two more circuits, each rated 10A, one designated “Ignition” and one designated “battery”, the latter of which remains powered when the vehicle is turned off.
What I wonder is if a load on that “battery” line will discharge the system beyond being able to start or if it will be shut off before the battery capacity drops below a level necessary for starting the vehicle.

 

[J Sierra]

I am the creator of the oscilloscope captures that show the ESS event.
Battery means connected to the battery (with fuse), so yes a load will drain battery until dead.

 

[Lo Tek]

I am the creator of the oscilloscope captures that show the ESS event.
Battery means connected to the battery (with fuse), so yes a load will drain battery until dead.

Thanks! I didn’t find a clear diagram that showed this circuit so hoped someone knew for sure before I started tracing backward from the fuse.

Sponsored