Strange Electrical Issue

Basil48192 · May 26

Sorry for the long post, but I experienced a strange electrical issue over the weekend and am hoping someone might have some insight.

I have a 2021 320S with two, 235 AH, 6 volt, AGM batteries. They are about 4 years old and have worked very well....as most of my camping is off-grid.

This weekend was my first trip of the year.

I left on Thursday morning with fully charged batteries. I used the water pump, lights, heat, and refrigerator 'on and off' once I got to my campsite.

On Friday morning, I noticed the reading light in the back of the camper would 'dim' slightly when the refrigerator kicked on....something I've never noticed before.

Again, on Friday night I ran all of the items listed above with no issues...though I didn't really pay attention to the lights.

On Saturday evening, I took a shower so the pump was running more than usual. In the middle of my shower, the pump slowed and the lights in the camper dimmed and eventually went dark. Once out of the shower, I checked my Victron Battery Monitor and it read 83% charged.

It seemed that when multiple items were running, the power would drop significantly. I was worried about the 'brown-out' damaging some components so I shut everything off for the night.

The system seemed better this morning, so I turned the refrigerator back on for the trip home...assuming that power from my TV would suffice. Right now, I am home and the battery level is down to 80%...which is typical for a 4 day trip with very little solar regain (it was mostly overcast). I did a quick check by turning on an interior light and then turning on my pump. The light flickered very slightly....but never really dimmed.

Lastly I plugged into to 'shore power' and did the same test. The light did not flicker or dim at all.

My first thought was that my batteries are starting to fail, as I am beginning my 5th camping season with them. However, the monitor shows that I have a sufficient charge.

Tomorrow I will remove the battery cover and check all of my connections.

Questions:
-Can againg AGM batteries show an 'adequate' charge, yet still not have enough capacity to power multiple devices at the same time?
-What kind of tests can I perform on my batteries to determine their overall health?
-Are there any common, 'vulnerable' places to check for poor connections?
-Any other comments or suggestions?

Thank you in advance. Any comments will truly be appreciated.

TourDeForth · May 26

If you have a volt meter you can measure the internal resistance. A failing battery can have a high internal resistance. A large voltage drop under load will also be an indication. But to be sure or confirm your results a battery tester should be used. Most auto parts stores will test a battery for free. But, getting heavy batteries out and down to the store can be a chore. Some stores will let you borrow or rent a battery tester.

jjfalardeau · May 26

I had a similar problem once where my shunt indicated good charge, but the reality was batteries were almost fully discharged. Turned out my positive battery lead was faulty and not torqued correctly. Replaced cable and tightened all bolts to spec. Maybe not your issue but something to check.

Basil48192 · May 26

@TourDeForth and @jjfalardeau. Thank you both. I'll try both suggestions.
Laying in bed thinking about it (sad...I know!), I wonder if my pump was acting up and drawing way too much current. It seems like it would have blown a fuse if that were the case. I'll check to see if the lights (that were affected) were on the same circuit as the pump.
Thank you again.

Basil48192 · May 26

One more hint/question.
I plugged into shore power around 8:00 PM last night and battery monitor read about 79%. At 8:00 this morning....I'm only up to about 95%. Maybe I'm being paranoid, but it seems like it should have been fully charged by now.
Thanks again!

rfuss928 · May 26

Basil48192
When the Smart Shunt was initialized the installer/user defined the battery capacity and 100% SOC during the set up. The Smart Shunt counts amps in and out to determine the remaining capacity of the battery.
The 4 year old AGM batteries are likely degraded to 50% or less of their original capacity but the Smart Shunt is still using the original programed value for its estimation of remaining charge.
IMO - It is likely time for new batteries

Basil48192 · May 26

@rfuss928. Thank you! I'm guessing you're right. Now that my batteries are back up (around 100%), I don't get any flickering at all. 4 years goes by pretty fast!

Grumpy_G · May 26

-Can againg AGM batteries show an 'adequate' charge, yet still not have enough capacity to power multiple devices at the same time?

Lead-acid batteries lose capacity as they age but they will still charge to the full design voltage of 12.6 V. They might even "pass" a load test with a simple tester that applies a 100 A load for a few seconds (10 seconds at 100 A is only 0.27 Ah). Yet they might only have 20% of their original capacity.

-What kind of tests can I perform on my batteries to determine their overall health?

The best way is to do an actual capacity test by pulling a constant current and monitoring the battery voltage. Amazon has simple devices that will draw current until a configurable low voltage cutoff point is reached and just multiply current by time into Ah. The same could be done with a (smart) shunt that measures Ah or Wh by turning on some lights/devices in the trailer but the voltage needs to be closely monitored to not over-discharge the battery. Note LiFePo batteries turn themselves off so watching the voltage is less critical, I actually tested mine by turning on the 3 way fridge on DC which is a 10 A load and just let it run until the battery turned off.

Basil48192 · May 26

@Grumpy_G. Thank you! I think I'll buy the Amazon tester. I just checked all my connections (under the battery box cover). My batteries and the connections look like the day I put them in! All connections are tight and clean.

If I can ask one more question: Are AGM batteries subject to the 'battery memory effect', like the old NiCad rechargeable batteries?
Most of my 'off grid' camping are short, 3-4 day trips, so I don't think my batteries have every discharged below 65-70% before getting home to recharge fully.

Thanks again!

Basil48192 · May 27

Sorry...a little internet search and I found that AGM batteries are not subject to the battery memory effect.

pthomas745 · May 27

@Basil48192 If your batteries are still holding on fairly well after 4 years, good for you. That means you have done a reasonably good job of not letting them drop too low too many times, and haven't let them sit at a low voltage for a long time. Sounds like you have done a lot of things right and got your money's worth from these batteries.

Basil48192 · May 27

@pthomas745. Thank you, I baby my camper and have had very few problems. Now the search for replacement batteries! I'm sure I'll go with lithium....just based on the expected lifespan.

Thanks again for all the support. This is a great group!

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