Possible AGM battery replacement

Jetman · March 2023

Have a 2018 400, I just bought and I think the two 6 volt AGM batteries are original. They on shore power show 4 dots on the control panel inside. When remove shore power within three days lights on panel will go to two, nothing on in camper. If cut disconnect switch off very little change.

i have not removed the cover over the batteries to see what amperage/ brand they are. Question is once remove cover how do I check voltage to see if good or bad? If need to replace, what type of AGM Is preferred brand, how to make sure installed properly, and can I use a trickle charger on these types of batteries as I did with 2015 320S with wet battery. Not much room where they are under the bed and with the battery disconnect switch.

Thanks for any help rendered

jetman

pthomas745 · March 2023

This will call for a multimeter. Any simple multimeter from Harbor Freight or the many available from Amazon. They are easy to use, and we can show you how.

The battery monitor, when the trailer is on shore power, is reflecting only the charge going into the battery from the converter. This is a "false" capacity reading. When you unplug from charging, the battery will start to discharge due to what is called "parasitic drain." There are items in the trailer that always draw some power, such as the Jensen TV and stereo, and the gas detector. Added up over a day, that might be somewhere around 7 amps (I'm guessing). Over three days, that would be about 21 amps. Your dual 6v battery setup gives you "about" 120 amp hours of "usable" power. The "lower" number of "dots" on the monitor reflect this parasitic drain. The monitor in the trailer also suffers from "false" voltage readings if the trailer battery is "in use". Since your AGM batteries are being drained very slowly, the voltage reading will be lower than the actual voltage. The trick here is to use a multimeter, with the battery switch off, and the trailer unplugged from any incoming charging source. If you go into the trailer and crank on the fan to high, you can see the trailer's monitor react by dropping even lower. (This is normal...)

So, find a multimeter. Looks like rocket science, if you have never used one. But, not really hard. Here is a stack of Amazon meters for less than 25 dollars. As you get further into batteries, you will hear about Victron shunts and other things that will make this a little easier.

https://www.amazon.com/multimeter/s?k=multimeter&rh=n:228013,p_36:1253528011&dc&ds=v1:0KL5LjQfoLN1zLdmIyBf5rE62CwsamO7mosDxYFYY5Y&qid=1678686816&rnid=1243644011&ref=sr_nr_p_36_1

Horigan · March 2023

@Jetman
There is a small junction box next to the battery under the bed that is connected directly to the battery. You can use this to measure the battery without taking the battery cover off. Take the junction box cover off and you'll see both battery wires coming to terminals on each side. Be very careful not connect/touch both terminals together as they are very close to each other.

To check your battery health, I would charge the battery fully, then turn off the battery switch. After letting the battery voltage settle for at least an hour, check the voltage with a multi-meter at the junction box. Then check the voltage again a day or two later. Good AGM batteries have very low self-discharge, compared to lead-acid batteries, so you should not see any significant voltage drop over the course of a few days with the battery switch off. If you see a voltage drop, you're battery(ies) needs to be replaced. Given their age and the readings you're seeing on the trailer monitor, they are likely toast.

The battery capacity for the dual 6V configuration is 224Ah (amp-hours), so useable amp-hours is half that, as noted above.

MuttonChops · March 2023

@Jetman ; @Horigan and @pthomas745 have provided the details you should need.
This comment/response is just to provide some additional visual / diagram reference points for you.

Typical DC Distribution Block Horigan referenced:

Typical Battery Wiring.
Note when you measure the Battery Off Voltage any solar panels (if installed) must also be Off
which may require your pulling the solar panel in-line fuse(s).

Image: https://us.v-cdn.net/5021717/uploads/editor/d7/410cvim0yymv.jpg

Jetman · March 2023

thanks for the info and the photo, I will get a multi meter and see what’s going on.

if do need batteries any suggestions as to brand and where to purchase ?

bergger · March 2023

If you want to stay with AGM to keep the swap easy and simple Harris is a good battery and is what came in our 2021 400. It has two 6v wired in series. They have been great and with our solar we have never come close to even 50% capacity. Trojan is also a very good choice. I've also had a Trojan battery in an old trailer and liked it very much.

Here are the specs on the battery NuCamp used for a while. A single lithium is now the standard.

Jetman · March 2023

Thank you for the help

JamesC · March 2023

I also have 2018 400 and just changed out the two AGMs to a single 200ah lithium battery from Renogy. The change also required a new converter that would charge lithium correctly. I used the WFCO model

WFCO WF-8955LIS-MBA with a switch to change from LA to lithium. Not a difficult thing to do even for an electrical idiot like myself.

It also allowed me to delete the battery box, reduced the weight and makes monitoring the battery easier because it has Bluetooth built in.

I also installed a Victron battery monitor previously so there are multiple ways to monitor battery usage. And it all fit’s very neatly under the bed!

bergger · March 2023

Has anyone determined if going from 130lbs of AGMs to about 60lbs of lithium increased the hitch weight very much? Just curious.

Horigan · March 2023

You could do the math. Measure the distance from the axle to the battery center of mass, and the distance from the axle to the hitch. Multiply that ratio (batt distance/hitch distance) to the battery weight reduction and you get the tongue weight reduction increase. Given how close the batteries are to the axle (2018 & 2019), I suspect the tongue weight reduction increase is small.

Edit: I corrected my terms above and measured my trailer. The ratio is 1:7 for the 2018/2019 400s, so the 70 lb weight reduction of the battery will result in a 10 lb increase in tongue weight.

Possible AGM battery replacement

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