Red battery lights on panel? 2024 Micro Minnie 2108FBS

[Wmlunt]

2024 WBGO MM 2108FBS
Hey guys,
What do the 4 red lights on the main panel for the battery actually show?
Dry camping for the first time and not sure how long the batteries are going to go keeping the compressor style refrigerator running. We have (2) 110 aH Lithium and don’t want to drive them to zero.
Has been almost a day and we still have 4 lights showing. I read on the forum that fridge will suck 80-100 per day, which might leave me at 50%
Do they stay at 4 then drop off like a rock?
Waiting for another day to get a grounded neutral plug for genny. Also sounds like a shunt is in my future…
TIA for any advise!
Bill

[creativepart]

Can I suggest that if you're going to dry camp with 220ah of LFP batteries that you go one step further and install a shunt-based battery monitor.

The "Lights" in your battery monitor indicate voltage and since your RV came with LA batteries it would be looking for those voltages - not necessarily the higher voltages your LFP batteries operate at. (FYI, LA = Lead Acid and LFP = Lithium Iron Phosphate)

A shunt battery monitor connects between the main neg battery post and the neg load cabling that usually connects there. The shunt monitors all current going into and out of the batteries and can provide an accurate state of charge in percentages.

A fully featured device like the Victron SmartShunt is a great choice for about $100 that uses Bluetooth to relay all that info to an app on your smart phone.

No more guessing about what a few little lights mean for your battery condition.

https://www.amazon.com/Victron-Energ.../dp/B0BF636VBX

[eatSleepWoof]

There are two main battery types found in most RVs:

1. AGM/flooded/lead acid
2. Lithium

You have #2.

Batteries in group #1 put out just over 12v, and this voltage decreases as the stored energy is consumed. Using a 100ah AGM battery as an example, by the time you use up half of it (50ah), the voltage will have dropped to about 10v, which is too low for any 12v appliance to run, and this is considered an "empty" battery. The battery monitor you are referring to in your post operates on this very premise - it measures the voltage and based on the reading, it shows you the appropriate state of charge via those lights.

Batteries in group #2 typically put out anywhere from 12-15v, and have much more "usable" capacity (vs. group #1). This capacity is typically in the ~95% range (vs. 50%). So your 110ah lithium battery will allow you to use about 105ah (double all numbers for your two batteries), and the whole time, the battery will output more than 12v. Combine this with the battery monitor you have, and that monitor will continue showing full charge, because it treats anything at or over 12v as "100% charge". In practice, once you use up that 95% capacity, the voltage will drop significantly, and your battery monitor will go from "100%" to "0%" in an instant.

The proper way to monitor battery charge is to utilize a negative battery shunt, as creativepart mentioned above.

--

We also have a 2108 with a 12v GE, compressor fridge. I've installed 200ah of lithium.

We typically arrive in camp around 3pm on "day one," and the following morning (7-8am) we have anywhere from 40%-60% battery left. In our use, the vast, vast majority of electric consumption is the fridge.

Without recharging you'll have about 48hours of camping before your batteries are fully drained.

[Wmlunt]

Thanks guys, I thought about 2 days was pushing it, found a power panel nearby with a receptacle so I am borrowing some power until I can get my genny parts (grounded neutral plug, and new 30a/15a pigtail) from Amazon.
I can see when solar charger switches over from bulk to float as ruff indicator as well. Just don’t want to go too low that the lithiums won’t recharge.
I am familiar with the battery types and like I said a shunt is in my future, likely next season at this point.
I engineered 6000 deg kelvin furnaces for LFP for car batteries as well as other lithium types, the only domestic source for lithium and reprocessing used lithium in the US!
Thanks again! Bill

[creativepart]

https://www.youtube.com/watch?v=zAS_ONuUJqk

[Wmlunt]

Thx creativepart!
I had considered building a plug, darn easy for me as an engineer but decided that a fully sealed and potted device for $8 to plug into the genny outlet was the way to go, less issues of shorts, etc.
I have been looking at the victron shunt to go with my victron solar chargers, since the spring, but we spent almost 3 mos touring the US and really don’t like to mess with stuff while on the road.
Bill

[Wmlunt]

I think I have my temporary solution with some help from folks above!
My Victron solar charge controller reports battery voltage via Bluetooth on my phone. I believe I can use that and the attached chart to give me a percentage of power left, without having to use the red idiot lights.
Not as convenient as a shunt reading out in percentage, but it does eliminate at least a couple potential failure connections that the shunt would introduce…
I can likely graph the response to see how linear it is, ruff number is likely good enuf for us. I would err on the side of caution and ensure we don’t drive the LFP too low to recharge easily.