voltage drop in storage?

[Airslide]

My stereo stayed on too.. but when i held the off button down for like 5 seconds it totally shut off..

[Gene]

Holding down the "off" button until all the lights go off on our stereo is the way to really shut it off. Otherwise it shuts off the radio or whatever, but messages keep going on the front so something's going on in there. Took me a while to figure out you have to hold down the button to actually turn it off.

The battery disconnect switch and light are mystifying since the light stays on when the switch is off in certain combinations of things (I can't remember what combinations, sorry, I'm old). My light never went off and there was a short somewhere which was fixed on warranty.

I checked my batteries with a new specific gravity tester and all the cells read perfect. So I unplugged shore power and only the solar panel will charge it. I'll see what the readings are after several days. I know I am hoping the batteries are no good so I can get better ones, but then I realize that will cost me money. It's so hard to be conflicted.

The electrical things on my trailer are even more confusing than on a car. I can usually figure it out after a while (which often includes a lot of bad words), but never really feel comfortable. The instructions for various things usually are written to be understood only by the electrical engineer who invented the thing and no mere mortal.

Gene

[hshovic]

I also have the chart for voltage and charge as given above.
However, it is at 70 deg F. Battery voltage at full capacity lowers with temperature. And so does capacity (about 30% at 30 deg F).

So when monitoring battery voltage to determine how much capacity I have, the temp must be factored in. The web has a bunch of charts on how to do that. At 70 deg, 100% capacity is 12.6 or 12.7. At 70 deg, 50% capacity is 12.06 volts.

But at 40 deg, 100% capacity is 12.3 volts. At 40 deg, 50% capacity is 11.76 volts, and the total capacity is down 25%.

Sounds unfair , but it seems true. Batteries work better when warmer.

The AS battery monitor does not recognize this subtlety, nor do most inverters, so sometimes my inverter will not work, even though capacity is still up there, and the AS battery monitor goes orange, even though I have capacity left.

[bryanl]

IMHO Rvers don't need to use hydrometers with their attendant hazards on modern batteries. Touchy topic for some, though. I don't know why.

Batteries may have more capacity when warmer but they don't live as long. Heat will kill batteries.

The AS battery monitor does not recognize this subtlety, nor do most inverters

This can be a big deal in storage as it makes a proper float voltage rather tricky. It is one reason why I think the PD+CW or WFCO approach works. That is to keep the float a tad low to avoid boiling off electrolyte but to bump it every few hours top up the charge and circulate the electrolyte.

[Gene]

Hank, those unfair batteries send me contradictory readings when it's in the 20's. The solar monitor has lower readings than the Airstream monitor. This is my second monitor as the first one worked for a while, then went crazy. As a result, I don't particularly believe it. Anyway, the solar monitor reads battery voltage (among other things) and can easily go to 50% or lower late at night with the furnace fan on while, the Airstream monitor is telling me the batteries are at a higher charge—maybe 3/4.

So, the unsophisticated Airstream monitor gives readings that are higher when it's cold and that's why I'm getting 3/4 when the solar monitor is reading much lower. If I understand what you're saying, the Airstream monitor reads higher than actual voltage when it's cold. Or have I got it backwards? If I've got it right the solar monitor is right on and that tells me why I'm not getting the charge when it's cold from the solar panels that I expect—maybe. It seems to discharge quickly the colder it is, or maybe quicker than I remember from a year ago.

Certainly the info about voltages at 40˚ vs. 70˚ is good to know and thanks for that.

Gene

[bryanl]

also keep in mind that voltage (or specific gravity for that matter) readings are easiest to interpret on a quiet resting battery.

I find that a good half hour or more of no significant loads (e.g. furnace, water pump) or charging is good enough for a rough idea about my battery state of charge.

[hshovic]

Gene,
That's just the opposite of mine. Lower temperatures mean lower AS monitor voltage than measured on my solar. I know the solar may read high in the sun, so I generally check it when it is dark.

Or I could just quit going out so late in the year....

[agbliss9615]

Just put two new T105 Trojan 6 volt batteries in my 08 International to replace the Interstate series 24 batteries. Had a local welder cut the bottom off the battery box and weld in a 3" strip of metal all around. He did a great job ($112) and I painted the new bottom with touchup paint from airstream. Looks and works great. Went from 160 amp hours to 225.

[Phoenix]

A few comments:

1. The OEM batteries that come with a new Airstream aren't the best and won't last very long. One battery lasted a year in our 2005, 19-foot Bambi, and the other one pooped out about six months later. We replaced both with Optima deep cycle (blue-top) batteries, which should last much longer. They have more capacity, hold a charge longer, and are slightly smaller than the batteries they replaced.

2. If I recall correctly, the propane sensor still blinks when the storage switch is turned off; and there appears to be other electronic devices that may also drain the batteries. We installed a separate, Perko (marine) battery isolator switch, commonly used on boats, that completely disconnects the batteries from the trailer. It is also nice, in case you have one weak battery and the other is still usable (assuming you discover this before the bad one discharges the other); because you can switch from using battery "A", "B", "BOTH", or "OFF". In the "OFF" position, both batteries are completely isolated from the entire trailer (and each other), and the only drain will be the internal resistance of each individual battery.

Since we installed the Optimas and the marine battery isolator switch, we have had absolutely no battery problems. We leave our Airstream connected to 110 AC all the time, so that we can use the lights, etc.. And, once or twice a month, and before we take it out, I turn the battery switch to "BOTH" overnight, to top off the charge.