Charging the AGM "Kicker" - 2021 Zion Slumber w/ Lithiums

[BenHennig]

I have a 2021 Zion Slumber with lithium coach batteries. The coach's lithium batteries are accompanied by a so-called AGM 'kicker' battery which runs the Firefly and some other functions whilst the lithiums are disconnected.

I'm trying to setup a trickle-charger to maintain the coach AGM 'kicker' during the winter. The lithium batteries will be shut off (via the Firefly), so to my knowledge, they shouldn't see the trickle-charger. I expect to be able to figure out the connections and would rather use the charger than to have the inverter run from shore power all winter long.

Question: How do you make the physical connections between charger and house kicker AGM?
- Crawl under the coach and start splicing into wiring? Not very excited to rig this up.
- Can you get direct access to the AGM battery terminals under the coach? Or do you have to remove the battery? I understand the battery is located just in front of the rear axle.
- Connect to the inverter terminals inside the coach? Note: the terminals are not exposed so I expect I'll be disconnecting the cables from the inverter to get access.

Thx!

 

[Rich W.]

Can’t answer that (no experience with Roadtrek) but could you take a look at this thread: Lithium batteries jump start ?
Maybe you can shed some light on that issue.

On your issue, my first choice would be to connect the charger right to the AGM battery terminals if they are accessible.

 

[BenHennig]

Thanks Rich. That didn't quite address my challenge though. Appreciate the link.

 

[BenHennig]

To follow-up...
I used the inverter terminals to charge the AGM battery. There is a simple cover on each terminal, removed by a hex key, and then a thumb-screw (aided by another hex key) terminal post. I was able to connect my charger there.

I turned the lithiums off to ensure they didn't see the charger voltage. The coach battery needs to be not disconnected of course.

Unfortunately for me, my AGM is wrecked due to being drained too much over the winter. I had it tested at the store and they confirmed it was dead. I had measured rather low voltages as 10.x and 11.7v, so I'm not surprised. I'll be using a smart battery tender (NOCO GEN5X2) in the future to keep it (and the chassis battery) charged (but not overcharged) during periods of inactivity. $300 for a replacement battery. Existing P/N is 8A31DT: 12V, AGM, group size 31, 1000 cold-cranking amps, 210 min reserve @ 25A, 105Ah. I replaced the old one myself which was not particularly fun given that the battery weighs about 75 pounds. Definitely need a lift of some kind to lower/raise a battery in place. The battery is located just in front of the rear axle.

 

[Rich W.]

Yup a GP 31 is a big battery and with current (inflated) prices, I’m not surprised that it was $300. The labor would add a chunk too. And this is really the responsibility of Roadtrek - a proper system design wouldn’t allow this to happen. Sounds like the tender/smart charger is a good fix as long as you have power. Have you thought about installing a battery disconnect for the AGM?

 

[BenHennig]

I have not considered a battery disconnect. I just don't understand the system wiring well enough to know where to insert it without going down the rabbit hole (further).

 

[RTroad]

Hi Ben,
You are very knowledgeable! Can I ask you a question? We have a 2023 Roadtrek with an AGM kicker battery and are wondering how to best maintain it over winter. Our manual says to switch off the 30-amp circuit breaker if we store the Roadtrek for an extended period. Does that make sense — would it help keep the AGM from draining? If not, do you know why they suggest it? We plan to ask our Roadtrek service folks about this, but appreciate any experience or insights you gave on this. Thanks!

 

[BenHennig]

So I have to admit I'm not familiar enough with the details to give you clear assurance.

I do recommend using a battery tender designed for your battery technology. I'd also connect one to the chassis battery in front of the driver's seat (or there are also connection points under the hood). The benefit of something like the NOCO GEN5X2 is that it can monitor and charge two batteries independently and tailor each charging profile for different battery technologies. Letting the AGM discharge too low can result in its failure requiring replacement. I have had to replace both my coach and chassis batteries at about $300 each because I wasn't using a battery tender over winter.

I tend to follow the manual and disconnecting the breaker seems like good guidance to at least reduce drainage, if not prevent it entirely. Personally, I'd do just that but I'd also use a battery tender. When you connect the tender and have the breaker open, I'd look for some evidence that the battery tender it isn't rendered ineffective by the open breaker. (Meaning, depending where you connect the tender, the charging current could possibly be blocked by the open breaker, unless of course you climb under the vehicle and connect directly to the battery terminals.) I doubt that would be the case though. Evidence could be that the charger is indeed supplying current, or that the charging lights are cycling as would be expected.

 

[RTroad]

Thanks! That’s helpful. We use a trickle charger to maintain our RV’s car battery - so a great suggestion to get one that independently charges and monitors two batteries. Didn’t know those existed!

We had a 2014 Roadtrek and had to charge it’s AGMs over winter. This “kicker” AGM is a new twist, especially given lithiums need to be warmed first to charge. Hope you are enjoying your Roadtrek! We really like the new Roadtrek with lithiums. I’ll post a follow-up if we learn something interesting from the service folks. Thanks again!

 

[dilbertjth]

Thanks for the part number and specs. I may be replacing mine soon. It charges up, but doesn't seem to hold it long. I'm going to try a couple of solar battery minders, one for the AGM and one for the chassis battery.

Does anybody know if the rooftop solar panels will charge the AGM when the disconnect switch is in the disconnected state? I assumed they would not, and have my Zion SRT covered. But if they do, maybe covering it is a bad decision. Seems like a waste to have 330 watts of solar panels not doing anything to keep any of the batteries charged over the winter.

I'm also wondering if anybody knows where a complete wiring diagram can be had. That might be helpful in answering these types of questions. Thanks!