state of charge - deep cycle RV batteries

KGs2108DS · 06-10-2024, 08:22 AM

2018 MicroMinnie 2108DS - two deep cycle marine batters 175 tot cold cranking several years old. Use VictronConnect & app to monitor. Batteries are NOT (apparently) charging fully as they should - yesterday 500mi/9hr and arrival home state of charge 82% (79% when leaving CG). only thing running is fridge (Dometic - running on LP DM2652RBX). have screen shots of battery data, but cannot figure out how to post/attach (apple iPhoto) URL. Fridge uses about 1amp, batts were down about -22Ahr when leaving CG yesterday AM. Oddly, graphical display of amp hx shows draw up to about 4amp draw from 4p to 9p while towing.

**creativepart** · 06-10-2024, 08:58 AM

Here’s the thing, marine/deep cycle batteries are not really deep cycle batteries and cold cranking amps don’t matter when discussing battery capacity.

If so they would need to be 85 amp hour batteries to yield 170 amp hours. There are 85 amp hour Group 27 batteries but it’s not that common in marine “deep cycle.” If you have the battery specs look for the 20-min amp hour rating, not cold cranking amps, which are instantaneous amps for engine starting.

But that aside there are many possible reasons your batteries didn’t fully charge or show fully charged in the Victron app after your drive. The most common would be low charging voltage from your tow vehicle. And another possibility could be incorrect settings in your Victron shunt leading to incorrect readings in the app. If the shunt settings are not correct you can’t trust any of the readings you are counting on.

It’s also not at all uncommon for those batteries to have lost significant capacity if they’ve had a rough life the past few years.

Can you provide more info about your batteries? What Group size are they? Do you know their history or are they new to you? Same with you Victron shunt. Did you install it and set it up?

Once we know a bit more perhaps we can provide better insight into what’s going on.

**creativepart** · 06-10-2024, 09:03 AM

Quote:

Originally Posted by KGs2108DS

have screen shots of battery data, but cannot figure out how to post/attach (apple iPhoto) URL.

You can’t add images with a URL that way. You must upload them to our forum as attachments to your post.

Here is a link to the instructions:

https://www.winnieowners.com/forums/...ml#post3773760

Morich · 06-10-2024, 10:40 AM

If no recent changes made and things were working correctly, I might lean toward checking some less complex things!
The connections from tow to trailer are out in the weather as well as exposed to all kinds of potential damage, so I might look them over as a reasonably simple start.

When you have the tow vehicle running at highway type speed, do you get a full 13+ voltage at the battery posts? For current to run in to the batteries, we have to have a voltage somewhat higher than the normal charge we expect from a fully charged battery.
Current flows from higher to lower voltage, so if the difference in that "hill" drops to much, less and less current will flow.
One way to reduce that current flow is if we get some form of resistance in the path from the engine alternator to the toad batteries.
Slipping fan belt on alternator? Corrosion or poor contact at numerous places along the path? Even something as simple as corrosion on a connection.

We get a lot of posts about trailers that have electrical connections down under the frame at the front where we have to look up from under near the propane tanks.
If you have that setup, it seems to be a terrible plan to put that many breakers, etc. almost directly in any water from the road, so they tend to be a corrosion problem!

Perhaps try comparing the voltage of the tow vehicle battery to the toad battery as the engine is running. If there is a good bit of difference in the two, find where there is too much resistance in the line between the two!

KGs2108DS · 06-20-2024, 10:07 AM

thanks CreativePart and Morich! I'm gathering info re: the questions you've asked me to research, and I'll post when I've got the information. I greatly appreciate your expertise and help!

KGs2108DS · 06-20-2024, 10:10 AM

attempting to attach a photo

KGs2108DS · 06-20-2024, 10:12 AM

I browsed hx of charging while driving home, and noted this period of 4amp draw for several hours during towing. Only item running was refrigerator on propane, and exterior trailer lights.

**creativepart** · 06-20-2024, 10:28 AM

Quote:

Originally Posted by KGs2108DS

I browsed hx of charging while driving home, and noted this period of 4amp draw for several hours during towing.

I could be reading your chart wrong... but a 4 amp DRAW would be shown as a -4 amps, I think.

As I read it you have a ~4 hours period of charging and depleting followed by a !/2 -1 amp draw the rest of the time.

The shunt shows amp in as + and amps out as - At least that's how I read my SmartShunt graphic charts.

Morich · 06-20-2024, 12:11 PM

Yes, I would agree that the upper point is charge going in and the negative as times when the charge was being used or drawn out!

An it does seem to make some sense if viewed that way?
At first the charge current was gradually increased to top off some batteries, then charge level held steady at some limit that is set. When the batteries reached near full charge the current gradually backed down, possibly to avoid overcharging the batteries? The negative dip might be charge used out of the batteries while the engine was shut down at a stop, perhaps?
Then a short recharge period, beofre going back to full charge again.
I read it as the negative points being when charging was not being done and there was some amount of drain pulling power from the batteries with some variety as different items like lights turned no/off!

Can you relate the high points to times when you were driving and the low as times you might have stopped? The funny waveform at end might be something like a placeholder signal to show it is still working?

KGs2108DS · 06-21-2024, 07:11 AM

thanks again! My Truck going in for maintenance next wed and will be talking to tech further about these charging issues. last summer 8 pin charge cable got ripped out of receptacle on rear bumper (hit debris in roadway and didn't realize cable was d/c), and I'm wondering if the connection is NOT completely stable while towing. I've placed a safety cable from charge cable to truck to insure cable doesn't get ripped out again. Also, thanks for your thoughts on interpretation of the graphical data on the SmartShunt! I'll think further on that!

Morich · 06-21-2024, 07:37 AM

If the graph was done during a steady drive time, I would think it says the connection was good at times and charging happened but contact lost at other times and the batteries were then draining.
Maybe a quick way to spot any flaky connect at the plug would be to put a meter on the battery, have the tow vehicle running and then wiggle the connection as you watch the meter for any jumps in voltage.
One of the pins may have been bent/damaged so that it is flaky?