Let’s get something straight right from the start. Mr. Internet says if you really want to precisely keep track of your RV batteries, you need one of these:
If you get it from Amazon, by the time you get the connection kit and pay tax, it will run you close to $400. Then you have to install it.
I didn’t do that. I used a cheap voltage tester and an even cheaper hydrometer. And I had success.
I also ended up with a lot of figures that I don’t particularly trust. I asked Miss Calculate to look them over, but she declined. She just tossed that adorable red curl back up on her forehead, and said “I don’t do fudge. If you want fudge, try the ladies down at St. Olaf’s, on Saint’s Day.”
But I’ve come to believe that any discussion of battery charging involves plenty of fudge. And the more precision you get, the less accuracy you are likely to have. I do not mean any of my figures are intentionally false. It’s just that there are so many variables – in battery type and construction, in temperature, phantom drains, timing, surface charge, connection – that it is hard to know what the figures actually tell you about the deep innards of your batteries. Fudge factors tend to cancel out conclusions.
I have never tried the Xantrex Linklite, nor am I likely to. I just don’t trust precision in these matters. Your mileage may differ, and in any case there is a comfort in numbers appearing on a pretty display. They just seem so trustworthy. Besides, they wouldn’t put it out on the Internet if it weren't true.
Voltage Testers, as a class, should be ashamed of themselves. They pretend to tell you things that they do not know. In that they are the very model of the iconic Internet maven. In a practical sense, the readings are almost information free. Okay, if your reading falls below 11.9V, you probably need to charge up your battery. But if it reads 12.7V, that doesn’t mean you should stop. At 12.7V, one battery may run all your gadgets for 2 hours. Another may do so for 2 days.
So what are these readings good for? When the news is bad in every way, voltage testers can give you a hint that is so. But they won’t tell you when happy days are here again, or how to get there. Voltage testers are for people who value a false sense of security.
The battery hydrometer, on the other hand, is a simple tool that yields good results, but they are the devil to use. People just don’t like how easy it is to get that icky sulfuric acid all over the place. The hydrometer is not precise, because after all it is measuring the progress of ever shifting chemical reactions. It gives you a range of results, best read as “green, white, or red”. And it is frustrating to use because an accurate result means lots of waiting for chemistry to settle down, and having to isolate the batteries during measurement.
Who has time for that? On the other hand, what else you got to do?
Let’s face it. The battery hydrometer is nasty business. No instant gratification like with that wonderful Voltage Tester. And all the hydrometer reads is specific gravity. That’s all. But that’s important, because a low specific gravity means you have mostly water in your electrolyte, and a high specific gravity means you have mostly acid.
And acid is what makes it all work.
When I started this trip, my 5 year old golf cart batteries tested right up there at 12.7 Volts. And way down in the red on the hydrometer. That means I couldn’t get much work out of them. Effectively, they were on life support.
These were big batteries. And they were acting like small ones.
As I explained in an earlier report, the lead plates had become sulfated, and thus taken out of action. But it isn’t a matter of just adding more acid. The answer is to apply large charging voltages over a considerable length of time, and thus force that dead sulfate off the lead plates and back into the surrounding fluid – thereby getting back the acid your batteries started with when they were new. Or some of it, anyway.
Whew. Enough ancient history.
So here’s what happened in my little experiment last week with desulfation. There were 4 sessions, about a day apart. Each time I charged the batteries up with the PD 4645 converter/charger until the automatic routine tried to “taper off” from 14.4V to 13.6V. Then I used the “Charge Wizard” button to force the converter back to 14.4V for the duration of the session.
The sessions were 2,4,4, and 2 hours long. After each session I did a hydrometer test. I did it the same way each time, in a manner that suited convenience rather than accuracy. I did not disconnect the batteries for the test, but I did shut down all but phantom loads and let the batteries rest 30 minutes after charging. I did it this way because what I was after was not the numbers, but rather the change in the readings over time.
The results over 5 days were entirely and consistently positive. On Friday, July 19, I left the batteries charging for 21 hours, plugged into house current and letting the auto regime run its course. Nonetheless, the next morning the hydrometer was still slightly in the red, though the individual cells were consistent across both batteries.
On Saturday night and Sunday morning, I did the desulfation routine for a total of 6 hours. Afterward, the hydrometer reading was low but firmly in the white. After each of the following three sessions the reading rose steadily through the white and into the green. After the last session the readings for both batteries were at the very top of the green, and equal for all cells.
Success! And in the nick of time, because I was getting really tired of running the generator. This would have been a lot easier and less annoying to accomplish back home.
Nonetheless, I am pleased. Before, every day I would charge to 12.7V, and end up the next morning with 11.9V. After the last desulfation, the next morning the reading was 12.44V. I did no charging that day. The morning after that, after almost two days of use, the reading was 12.23V. I changed nothing in my usual routine of use. That I was aware of (fudge factor).
So I seem to have gotten back 2 new batteries, which can last at least two days between charges. And all it took was the PD 4645 converter, a $5 hydrometer, and a $7 voltage tester.
Well. It also took a degree of patience, a quality not everyone ascribes to me. It is rather a relief I don’t need to gin up any more of it for this purpose. Or even talk about it much any more.
Whew. At last, everything just works.
Please remember I was doing this with Golf Cart batteries. These are heavy duty numbers, able to take a lot of abuse. If you hook up a 10A dumb charger in boost mode to a cheap car or motorcycle battery and walk away for a day, you may really wish you had not done that. AGM batteries might not take it well, as easy outgassing is a critical part of the scheme.
You must watch what you are doing, especially if you don’t have the PD 4645 to watch out for you and shut things down when the batteries get hot or dry out. So don’t do that.
All that can happen with some batteries, according to rumor, but I saw no sign of it with mine. There was benign gassing. Nothing got hot. And that’s all I have to say about that.