Would you keep using these batteries in your 320?

riseandshine

After noticing slower than usual battery charging last camping season, I tested our batteries recently - the test results, battery specs and other details are below.

Questions:

1. Are these batteries working fine, but showing the first signs of aging (low viscosity), as they are 4 years old?
2. Is it normal for a battery's performance to slowly decline, even while the voltage results are in normal ranges?
3. If we would like more power anyway, maybe it's a good time to upgrade our batteries, BEFORE we start having major battery issues as they age?

Specs:

• Trailer: 2020 Tab 320S Boondock with factory solar and added Victron 712 Smart Shunt. No other electrical upgrades of additions.
• Batteries: Interstate 6V 225Ah GC2-ECL-UTL, two in series = 12V 225Ah total, 110Ah usable, installed Spring of 2020. Should last 4 - 8 years according to solar-electric.com/learning-center/batteries-and-charging/deep-cycle-battery-faq.html/
• Usage: Almost exclusively boondocking, 3 season use in the intermountain West (20-80F temps), often several nights at one site. 20 or so camping days per year. We've come close to 50% charge a few times on extended trips with cloudy weather, so we're considering a 206 Ah LiFePO4 replacement to double our Ah and give us plenty of power margin.
• Storage/maintenance: Battery disconnect is engaged for winter storage (~ 5-6 months) in storage unit (single digits F at times). Battery levels topped up with distilled water a few times per season. Terminal corrosion cleaned up and terminals coated with petroleum jelly a few times since 2020.

Test Results (left, right, and in series at 50F temperatures):

• Fully charged, no draw: 6.7V, 6.7V, 13.44V. Fully charged the batteries then immediately checked the voltage directly at the battery terminals with a volt meter, battery disconnect OFF (disconnected from trailer).
• Fully charged, minimal draw:  6.68V, 6.68V, 13.36V. Fully charged the batteries then immediately checked the voltage directly at the battery terminals with a volt meter, battery disconnect ON (connected to trailer).
• 8 hour voltage drop: 6.43V, 6.43V, 12.88V. After fully charged, both batteries were isolated from all draws and charging cables and let sit for 8 hours.
• Viscosity of each terminal: 220, 220, 205; 225, 215, 220, which is in the "fair" range, but close to red. Using an inexpensive battery hydrometer I measured the specific gravity of EACH CELL of each battery separately according to: youtube.com/watch?v=lcFrUJHNo2M
• Charging system: 13.74V. With batteries disconnected and shore power connected, I measured the voltage of the wires that usually would be connected to the battery for charging.

ScottG

1. At first pass your voltage measurements look pretty good, but without a point of comparison it's hard to say how much performance may have declined over time. One specific thing I notice is that the voltage of a fully charged unloaded battery will decline steadily until it "settles in" and remains relatively stable over time. (This may take longer than eight hours.) As batteries age, that settling in point tends to get lower and lower.

2. Yes, this decline is normal. A four-year-old battery may not perform quite as well as when it was new, but that doesn't mean it's ready for the recycler. The rate of decline depends on several factors, but it sounds like you use your batteries pretty gently.

3. That's up to you. I tend to be a gambler, and a cheap one at that, so I like to milk all the life I can out of my stuff. The worst "major problem" you might encounter is that one of your cells poops out suddenly (probably the one with the lowest specific gravity) and you find yourself in the boonies unable to get a full charge. More likely performance will just keep declining until it no longer meets your needs, and then you'll shop for a replacement.

riseandshine

Thanks Scott for your input. Maybe we'll see how the batteries do this Spring on a few trips before being too concerned about them. I'll likely add a solar port, solar cutoff switch/fuse and a second MPPT controller for our portable solar panel to help mitigate the slow charging problem. That will be much less time and $$ than a new battery, new charger and a big rewire project.

pthomas745

That NAZ battery FAQ is a great favorite!  I learned so much from that.

Sounds like you have treated your batteries the way they should be treated.  The only other thing that might cause your issue is battery sulfation.  But, as it seems your batteries have been well maintained, this might just be a wild guess.  There are a lot of battery "how to" sites that describe this.

https://www.crownbattery.com/news/sulfation-and-battery-maintenance

riseandshine

Thanks Thomas for the webpage link to crownbattery.com about sulfation. I was unaware that lead-acid batteries should not be stored above 75F. While it's common to remove LiFePO4 batteries for indoor winter storage, it seems uncommon practice to remove lead-acid batteries between trips and store them indoors to avoid heat. This is our first trailer, so we're still leaning more about power, maintenance and other fun RV stuff every year.

The trailer is stored in a storage unit, which helps moderate daily temperature swings, but it's common to have summer high temps in the high 80's and 90's nearly every day for three months. The webpage says that the rate of self-discharge doubles for every 10 degrees above room temperature. The batteries likely see temps above 75F every year for a three month period, at least during the daytime hours. 

We'll keep a close eye on the battery charge times and discharge rates during normal use on our first trip this Spring. Installing some extra solar, and/or taking our generator on the first trip seems like a good idea.

ScottG

I agree, @riseandshine; during the summer months there is no practical way I'm going to keep my lead-acid battery below 75F all the time. I do keep it fully charged when idle, and I bring it in during the winter so I can monitor it and top it up as needed.

Grumpy_G

Voltage means nothing when it comes to battery health. I have an old RV deep cycle battery that will charge and hold voltage, even deliver high current for a short time but can only deliver 5Ah before the voltage drops too low. A proper capacity test is the only way to assess the batteries. I'm not familiar with the Victron 712 but I assume it can record Ah or Wh. Fully charge the batteries, reset the Ah/Wh counter, put a decent load on the batteries and monitor the voltage. Once the voltage drops to your preferred level read the measured Ah/Wh. Note that the ubiquitous voltage/state of charge table found everywhere in the Internet are only valid for a specific discharge rate so you might need to adjust your load a bit.