Hygrometer for Battery Testing

CatDaddy · November 17

I may be one of the few people on the forum that has factory FLA (flooded lead-acid) batteries and is old enough to have a hygrometer for battery maintenance, so I thought I'd post this:

My 2022 TAB 320S Boondock came with two 6V, US2200 X2 Deep Cycle flooded lead acid batteries. These are the old-fashioned batteries that are not maintenance-free (aka "VRLA"). That is both a blessing and a curse.

It's a blessing, because one can pop the caps off the cells and use a hygrometer to measure the specific gravity which is directly related to charge level, which is much more accurate than by using the battery voltage. It also allows one to tell how each of the three cells (6V battery) is holding up.

It's a curse because one has to remember to "water" the battery which means adding distilled water to the proper level. This is done by fully charging the battery and then filling with distilled water as described in the battery manual.

I now feel justified in saving my battery hygrometer for 50 years...

Here's how the specific gravity relates to the state of charge (SOC):

Image: https://us.v-cdn.net/5021717/uploads/editor/1i/j55v1yr6e84r.png

ScottG · November 18

Ha. I've camped quite nicely for a decade on single group 31 FLA batteries. And I have both a hygrometer and a refractometer that allow me to monitor batter health and aging.

We're a dwindling (and possibly stubborn) cohort. I'll probably replace my battery in the next year or two. Maybe I'll drink the lithium ion kool-aid then. Maybe not. :-)

CatDaddy · November 19

Who ya calling “stubborn”?

I night go on a campaign to reduce the tongue weight on my 320S but it’s hard for me to justify the expense of the lithium setup right now.

elbolillo · November 19

ScottG said:

Ha. I've camped quite nicely for a decade on single group 31 FLA batteries. And I have both a hygrometer and a refractometer that allow me to monitor batter health and aging.
We're a dwindling (and possibly stubborn) cohort. I'll probably replace my battery in the next year or two. Maybe I'll drink the lithium ion kool-aid then. Maybe not. :-)

If adopting new technologies is "drinking kool-aid", then we as humans have been doing that for quite some time. 😉

We could go back to horse and buggy and kerosene lamps.

All in good fun...

Marceline · November 19

ScottG said:

Ha. I've camped quite nicely for a decade on single group 31 FLA batteries. And I have both a hygrometer and a refractometer that allow me to monitor batter health and aging.
We're a dwindling (and possibly stubborn) cohort. I'll probably replace my battery in the next year or two. Maybe I'll drink the lithium ion kool-aid then. Maybe not. :-)

If you have a propane fridge or you mostly camp with hookups I don't think there's a really big need to switch to lithium unless you have some other sizable power need (CPAP?)

For those of us with 12v fridges and infrequent shore power, its not so much "drinking the kool-aid" as it is "facing the music."

Horses for courses, and all that.

ScottG · November 19

All a bit tongue-in-cheek, folks. Although I rarely camp with electrical hookups, I do have the propane fridge. I rue the day when I need to replace it, but can't because they don't make them anymore. At that point I'll likely need to go to a two-way, and upgrade to lithium ion so I have the juice to run it.

I'm pretty sure there is a conspiracy at play here! ;-)

CatDaddy · November 19

Marceline said:

If you have a propane fridge or you mostly camp with hookups I don't think there's a really big need to switch to lithium unless you have some other sizable power need (CPAP?)

Even without a propane fridge, one can boondock for a few days with two, 6V, 230Ah FLA batteries. I know because I've done it. My 320S has two, 6V, US2200 XC2, deep-cycle (not AGM) batteries in series. They're rated for 230Ah each. If I only discharge to 50% SOC, that gives me 230Ah of capacity. They cost around $170 each. That is still the lowest cost per amp-hour available. The downside is additional maintenance, added weight and potentially less vibration tolerance. Supposedly, the Trojan version of these batteries are even better. Costco currently has an Interstate version of these GC2-size batteries on sale for $80 each but they don't get great reviews.

Lithium has lots of advantages but they come at a cost. That cost premium is coming down fast, but it hasn't reached parity yet.

When my current batteries die, I will definitely look into lithium batteries, but that is mostly because I want to reduce the tongue weight of my trailer.

The Renogy mini 300Ah LiFePo4 battery that is currently on sale for $850 is hard to beat but it is still more expensive per kWh than FLA batteries.

Towhee · November 19

@CatDaddy If you are wired in series to get 12 volts total then your total Ah are still 230, not 460. In parallel you would have 460 Ah @ 6 volts. Am I missing something 🤔.

AnOldUR · November 19

CatDaddy said:
My 320S has two, 6V, US2200 XC2, deep-cycle (not AGM) batteries in series. They're rated for 230Ah each. If I only discharge to 50% SOC, that gives me 230Ah of capacity.

Two 6

V 230Ah batteries in series will give you 230Ah at 12V. Half of that is 115Ah of capacity.

6V times 230Ah = 1380 watts
1380 watts times 2 = 2760 watts
2760 watts divided by 12V = 230Ah
50% of 230Ah = 115Ah

None of that says you won't get a few day of boondocking from 115Ah.

elbolillo · November 19

2 6V batteries at $170 each x 2 = $340.00 $340 divided by 115ah usable capacity = $2.96 per ah.
1 300ah Renogy at $850.00 divided by 295ah usable capacity = $2.88 per ah.

Mickerly · November 20

I still use oil lanterns. They work really well. I can ride a horse, but the trailer is happier with the car. I've camped with a single 12v FLA and had usable power leftover across a 3 day cloudy weekend. Pay attention to what you are doing. Buy the equipment that best fits your needs.

The price of Lithium batteries is falling rapidly. Now, many come with built in Bluetooth battery monitors. That reduces cost significantly and makes the installation more simple. I think this is a sign of better battery technology on the horizon.

If you think Lithium will help your situation, then it's a good idea. The prices are not going up, waiting won't hurt. If the switch in battery technology won't gain much for you, then don't waste the money. Lithium is not for everyone no matter how much you play with the numbers.

I'm not against new technology. There are several things with NuCamp products that could benefit from moving to this century. For us, Lithium is not worth the cost because the only benefit is less weight. There is other, less expensive ways to reduce 30lb.

P.S. I have a hygrometer also.

CatDaddy · November 20

elbolillo said:

2 6V batteries at $170 each x 2 = $340.00 $340 divided by 115ah usable capacity = $2.96 per ah.
1 300ah Renogy at $850.00 divided by 295ah usable capacity = $2.88 per ah.

Yep! My calculation was flawed. BTW, the Renogy 300Ah battery can be had for $760 right now using promo code NEWMINI300. That tilts it even further in favor of lithium.

CatDaddy · November 20

AnOldUR said:

Two 6V 230Ah batteries in series will give you 230Ah at 12V. Half of that is 115Ah of capacity.

6V times 230Ah = 1380 watts
1380 watts times 2 = 2760 watts
2760 watts divided by 12V = 230Ah
50% of 230Ah = 115Ah

None of that says you won't get a few day of boondocking from 115Ah.

Yes, my bad. I did the calculation for batteries in parallel. However, 6V times 230Ah is 1380Wh, a unit of energy. I agree with your conclusion. It appears that lithium is now less expensive per amp-hour than high quality FLA batteries. Yikes!

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