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Old 03-11-2018, 01:05 PM   #1
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Hydrometer reading vs gauge

Hi all - I've posted a question or two recently about adding a better gauge to our TT so that we can better monitor our batteries with the intent being to maintain battery health. Because of work, life, whatever I won't get that gauge installed before our upcoming 2 week camping trip so today I went out to check the batteries. The TT has been sitting unhooked from shore power for about a week or more with the battery disconnect switch in the disconnect position.

I have a hydrometer and since I got a lot of feedback in the past about my plug in volt meter being a poor way to check the batteries I figured I'd go with the hydrometer first and then check with the plug in meter. The results I got are a bit confusing so I'm tossing this up to the FR brain trust in the hope of getting some clarification.

I checked each cell in both batteries (dual 12V setup). In each battery most of the cells were in the "fair" range (1.21 - 1.25) but in each battery there was one cell that would barely move the float and one cell that would go to the top of the good range. Next I flipped the disconnect switch to give power to the TT and went inside to check the voltage on my plug in meter. The meter showed 12.7V

I;m not the battery expert but I figured with the TT disconnected from any charging for a week and the batteries isolated that the reading I would get when I flipped the switch would be accurate. Maybe that's not the case - I will do another check later to see if it is consistent.

So the questions I have are this - I am guessing that I have a bad cell in each of the batteries - have I got that part right? Since the other cells are fair to good, it would explain why when we dry camped the batteries discharged faster than I thought they should have. Full disclosure - I have not done the math on power usage and during the last trip, the furnace did run occasionally during the night since it was in the low 30's out.

Next question, why the big difference between the hydrometer and the volt meter?

As I said, we will be leaving for a two week trip in a week but all the CG's have 30A hookups so I don't see any real risk to running like this for the trip. Anyone see any issue with my logic? We really don't want to go spend $200+ on new batteries right now (plus I'm thinking of switching to 6V batteries so there would likely be some work required to get those set in the tray and wired up properly).

Thanks for the help!
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Old 03-11-2018, 01:26 PM   #2
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FYI, if you have a WFCO converter/charger installed, they never fully charge your batteries. You need a dedicated Automotive charger to top off the charge. Try one, and you will probably see much better SG readings. I just did a pre-season test of my 3 year old battery after using the car charger, and all the readings were near the top, with two slightly lower than the other four.
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Old 03-13-2018, 12:39 PM   #3
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The WFCO converter, if working according to factory specs, will fully charge batteries. The WFCO charges slower than most other converters because it spends little-to-no time in bulk mode (14.4V).

At 13.7V (normal mode), batteries that are significantly discharged could take over 12 hours to fully charge. WFCO keeps normal mode for at least 44 hours, ensuring a full charge. It then cuts back to trickle mode (13.2V) to maintain the batteries.

My WFCO converter never went to trickle mode, so it would eventually fry batteries if left plugged in for weeks at a time. I ended up replacing the WFCO with a Progressive Dynamics (PD) converter rather than getting another WFCO under warranty. There are only 3 differences between the PD and WFCO converters:
1) The PD converter works as per its manual.
2) The PD converter will hold bulk mode until the battery approaches 90%, then switch to normal mode. This makes charging the battery significantly faster when discharged below 90%.
3) The PD converter, when in trickle charge mode, does a daily short boost at 14.4V which is supposed to avoid stratification within the battery cells by causing a few bubbles.

A car charger does not have all 3 modes, and therefore is NOT recommended to be left on the batteries for more than a day or so.

For the OP, be advised most cheap multimeters have accuracy issues. Most only claim 1.5% accuracy on the voltage ranges, which means +/-0.18 volts when measuring 12V. In real life, many meters seem to read 0.1 - 0.3V high when reading 12V. I have never seen one that read low.

As for hydrometers, I don't know how consistent they are or how small a difference they measure. Since batteries that sit still do tend to stratify - the heavier solution sinking, and the lighter solution going to the top - how deep in the cell you take the sample can make a difference. A charger that has a short period of "equalization" gets rid of stratification through creating bubbles. Also, the vibration and shaking from rolling on the road does a great job of eliminating stratification. Even the wobbling and shaking from walking around in the camper is good enough.

I would guess from your specific gravity readings that your batteries are well along in their useful life. Even a battery that has had the life sucked out of it can have a 12.7V reading when fully charged. It's just that the voltage will fall very rapidly under load.

just my thoughts and experiences, hope this helps
Fred W
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Old 03-13-2018, 08:39 PM   #4
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Thanks for the info - I continue to learn more & more from the forum and that helps keep the fun in camping.

I think these batteries are reaching a point where they need to be replaced. Our next few trips are to CG's with hookups so no rush at this point. When I do replace them I think I will be going with two 6 volt batteries so I can get my outback camping fixes with some peace of mind.

Regarding the WFCO converter, it's sort of funny - our last TT had an IOTA converter and I added a plug in for about $25 that made it a 4 stage charger. I thought it was really cheap on Jayco's part to not just sell the TTs with that plug in. Now I have a bigger/more expensive trailer and a even cheaper converter.

Oh well... I still get to go camping
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