Battery reading

[MollyMac]

I am so new and now confused. What should my battery read when I press the monitor button. I have a FC25 FB with Group 24 w/converter 2 deep cycle 2 batteries. I am nervous that I have run the battery down.
MollyMac

[Wingeezer]

From memory, I think around 12.7 is fully charged, and about 12.3 is 50%

When your battery is being charged by the trailer you will likely read around 14v+.

The battery will stay high for at least a few hours after a charging session so you must wait a while to let it settle down before taking a reading to determine its actual state of charge.

[uncle_bob]

Hi

The real question is "what should the battery read at the battery terminals when read with a multimeter?". Reasonably accurate multimeters are quite cheap. The monitor screens on the typical RV are grossly inaccurate in many cases. Read the battery, check the screen and come up with the "offset" between them. Once you have done that (reads half volt high...) you can to a lot better working out what's going on.

Bob

[MollyMac]

When I got it from the storage place it was reading 12.1...I drove home to pack up. Checked it at 8:00 pm....it was at 9.1...very concerned

[dmbecke]

I had the same issue on a 2014 recently purchased
Sounds like you need new batteries
How long since their last charge?

[uncle_bob]

Hi

Charging off of the TV is not likely to be very effective. If you get a 10A current from the tow, that's doing very well (you might get zero). At a 10A constant rate (which you will never see), it will take 10 hours of driving to charge a "half dead" battery. That's all with nothing pulling current in the AS. If you have the fridge and a few other things turned on, you might double or triple that.

Plug in to shore power, charge for at least a day, see where you are at.

Bob

[OTRA15]

Originally Posted by MollyMac

When I got it from the storage place it was reading 12.1...I drove home to pack up. Checked it at 8:00 pm....it was at 9.1...very concerned

When you got 9.1 were there any 12-volt functions running? If so, turn everything off, wait an hour or so after shore power is removed per earlier comment, and then check again.

12.1 represents batteries at about 40% of capacity +/-. Below that more serious damage starts to occur.

The earlier posters and uncle bob have good advice IMO:

Originally Posted by uncle_bob

Hi

Charging off of the TV is not likely to be very effective. If you get a 10A current from the tow, that's doing very well (you might get zero). At a 10A constant rate (which you will never see), it will take 10 hours of driving to charge a "half dead" battery. That's all with nothing pulling current in the AS. If you have the fridge and a few other things turned on, you might double or triple that.

Plug in to shore power, charge for at least a day, see where you are at.

Bob

You can take the batteries into an Interstate battery store [assuming this is your brand] to have them tested. This Battery School site is good background reading:

http://www.batteriesnorthwest.com/ba...ool.cfm?TID=10

Good luck!

Peter

[fran&frank]

If you run your batteries down below 50% discharge you don't instantly kill them but you do reduce their service life. Just get them up to fully charged ASAP.-- Frank

[Rich W]

I found this article on the state of charge for batteries a while back. I've printed and put inside a clear page cover so I could add it to my AS book.

[uncle_bob]

Originally Posted by richw46

I found this article on the state of charge for batteries a while back. I've printed and put inside a clear page cover so I could add it to my AS book.

Hi

If you are going to get into the details of charge vs voltage:

1) The voltage readings on the monitor panels have been reported to be more than a half volt off in one direction or the other. Don't use those numbers until you have checked the readings against a good multimeter.

2) Voltage numbers matter on a *quiet* battery. Charging and discharging both distort the readings. Measuring through wires that are doing charging or running a load distorts the numbers. Wait at least a half hour after charging is done before reading voltages.

3) The voltages and the capacity of the batteries change quite a bit as the temperature of the batteries changes. For normal temperatures it's > 0.5V. A battery sitting out all day in the desert sun may be fully charged and have a voltage reading that is pretty poor.

So what's the answer?

One way to figure out how a battery is doing are specific gravity readings. They will give you another way to see what's going on.

A "better" way to figure out how much battery you have is a monitor that reads the current into the batteries, adds it all up and compares it to the current out of the batteries. They aren't perfect, but they are way better than voltage readings.

Monitoring battery temperature for charging is a *very* good idea. That will also improve your capacity / voltage estimates.

Get a multimeter. It will come in handy for a number of things. They aren't very large. A really good one is < $100. One that is "good enough" is < $20.

Lots to think about.

Bob