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Battery state of charge

Yahoo Message Number: 21249
I've only been RV'ing 2 years and must confess that after reading everything I can get my hands on, I'm still the ultimate electrical dummy. I marvel at you guys that spit out all these formulas, terminology, and knowledge of the electrical system on these coaches. I'm a little concerned about my batteries state of charge. I've been home now from the East Coast rally about 5 weeks. My coach IS PLUGGED into 50 amp service, but has not been started up in those 5 weeks. I thought the chassis batteries probably were getting a little little low so I put the multi meter to them and they showed 13.3, which doesn't seem bad for 5 weeks, the house batteries show 13.8 These are two AGM batteries. The Sea Level Monitor on the bath wall shows the house batteries to be 13.8. The Xantrax panel shows 13.8, in float mode, and 100%. This is while PLUGGED into 50 amp service. All seems o.k. until I decided to check them while the coach is UNPLUGGED. I did this thinking that the battery charger might be helping the three meters give a false reading. What I found is that the chassis reading did not change (13.3) and that seems reasonable. However the house batteries now show 12.3 on the Sea Level Monitor, the Xantrax panel shows the "battery state of charge to be 78% of full", and the multi meter shows the house batteries to be at 12.2. I'm confused (that's not to abnormal for me) in that I thought that as long as you were plugged, in the house batteries should stay fully charged. I never thought to check them while unplugged and this caused me the confusion. Anyone out there have any thought on this? Are my two AGM house batteries being left in a state of low charge, thus possibly shortening their life?. Is my charging system maybe not fully charging my house batteries.? There is nothing on in the coach while parked except the Hydro Hot set at 50 degrees that occasionally comes on to prevent freezing, etc. Thanks.

R. D. Vanderslice
Rockwall, Texas

06 Allure 470 no. 31294

Re: Battery state of charge

Reply #1 –
Yahoo Message Number: 21251
Batteries are charged by applying a higher voltage than normal across them. So 13.8 while charging and 12.2 with the charger removed doesn't sound all that unusual to me. In fact, the only reading which seems problematical to me is the '78%' state of charge. How long after you unplugged it did you get that reading?

If was a while (a day or more), then perhaps it really did run down that much. Or perhaps you are right and 13.8 volts is not enough to fully charge the batteries. I don't think AGM need water, but if they do, low water is the cause of many battery problems.

I've heard there is a fairly substantual draw on the atteries while parked even when 'nothing' is on. Certainly the inverter has a significant standby draw, plus all the electric gadgets keeping their memories current and those which are always on.

Note also that raw battery voltage is a factor of the chemical composition of the battery, so a 'multimeter' voltage meter is not the best way to measure a battery's charge. You want an actual battery tester, which has a load built into it, as voltage under load is a much better indicator than just voltage alone.

If it was a standard (wet) battery, I'd also suggest one of those battery liquid testers (hygrometer?). But I'm not sure if you can use on of those on AGMs.

Hopefully you've got something like an 'echo charger' to keep the chassis battery charged too.

John 04 Inspire 51078

Quote from: R\. D\. Vanderslice
>

I'm a little concerned about my batteries state of charge. I've
been home now from the East Coast rally about 5 weeks. My coach IS PLUGGED into 50 amp service, but has not been started up in those 5 weeks. I thought the chassis batteries probably were getting a little little low so I put the multi meter to them and they showed 13.3, which doesn't seem bad for 5 weeks, the house batteries show 13.8 These are two AGM batteries. The Sea Level Monitor on the bath wall shows the house batteries to be 13.8. The Xantrax panel shows 13.8, in float mode, and 100%. This is while PLUGGED into 50 amp service. All seems o.k. until I decided to check them while the coach is UNPLUGGED. I did this thinking that the battery charger
Quote
might be helping the three meters give a false reading. What I
found is that the chassis reading did not change (13.3) and that seems reasonable. However the house batteries now show 12.3 on the Sea Level Monitor, the Xantrax panel shows the "battery state of charge to be 78% of full", and the multi meter shows the house batteries to be at 12.2. I'm confused (that's not to abnormal for me) in that I thought that as long as you were plugged, in the house batteries should stay fully charged. I never thought to check them while unplugged and this caused me the confusion. Anyone out there have any thought on this? Are my two AGM house batteries being left in a state of low charge, thus possibly shortening their life?. Is my charging system maybe not fully charging my house batteries.? There is nothing on in the coach while parked except the Hydro Hot set at 50 degrees that occasionally comes on to prevent freezing, etc. Thanks.

Re: Battery state of charge

Reply #2 –
Yahoo Message Number: 21254
R D One thing to remember on batteries is that a fully charged 12 volt battery will sit alone at about 12.8volts. Yes, it will loose some small % over a period of time ( Weeks not charged ). Now it something is using the current in the battery, then you can expect to see a voltage less than the 12.8. The longer or the bigger the load, that number will become less over a peiod of time. The condition of your batteries will effect how they stand up to the load put on them. Now on the other side, charging, will always show something greater than the 12.8 volts. The state of charge will vary the voltage pending if it is in a balk or float stage. Float is the lowest voltage state you will see when charging but will always be above the 12.8. You can charge your system by plugging in and when you get to the float stage, unplug your coach. Now shut off your house batteries, with your manual battery disconnet. Let some time go by, like a couple hours, and then check your house voltage at the battery. With no drain on the system you should see 12.8 or a little more. This only tells you that the voltage is normal with no drain on the system. If the voltage is less then you could have a battery issue. A battery load check with a condition checker is probably required to know where you stand. Let me know what happens. Ned Herrmann

Quote from: R\. D\. Vanderslice
> > I've only been RV'ing 2 years and must confess that after reading everything I can
get my hands on, I'm still the ultimate electrical dummy. I marvel at you guys that spit out all these formulas, terminology, and knowledge of the electrical system on these coaches. I'm a little concerned about my batteries state of charge. I've been home now from the East Coast rally about 5 weeks. My coach IS PLUGGED into 50 amp service, but has not been started up in those 5 weeks. I thought the chassis batteries probably were getting a little little low so I put the multi meter to them and they showed 13.3, which doesn't seem bad for 5 weeks, the house batteries show 13.8 These are two AGM batteries. The Sea Level Monitor on the bath wall shows the house batteries to be 13.8. The Xantrax panel shows 13.8, in float mode, and 100%.
This is while PLUGGED into 50 amp service. All seems o.k. until I decided to check them while the coach is UNPLUGGED. I did this thinking that the battery charger
Quote
might be helping the three meters give a false reading. What I found is that the
chassis reading did not change (13.3) and that seems reasonable. However the house batteries now show 12.3 on the Sea Level Monitor, the Xantrax panel shows the "battery state of charge to be 78% of full", and the multi meter shows the house batteries to be at 12.2. I'm confused (that's not to abnormal for me) in that I thought that as long as you were plugged, in the house batteries should stay fully charged. I never thought to check them while unplugged and this caused me the confusion.
Anyone out there have any thought on this? Are my two AGM house batteries being left in a state of low charge, thus possibly shortening their life?. Is my charging system maybe not fully charging my house batteries.? There is nothing on in the coach while parked except the Hydro Hot set at 50 degrees that occasionally comes on to prevent freezing, etc. Thanks.

Re: Battery state of charge

Reply #3 –
Yahoo Message Number: 21259
R.D,

Looks like everything on you coachs works as expected (battery-wise).
When you're plugged in (and the charger is on), you'll see that your chassis batteries will remain steady at around 0.4V below the house batteries. Since our coaches have an echo-charger between the house and chassis batteries, the chassis batteries are maintained at a somewhat lower voltage.

The echo-charger is driver by the voltage differential between the 2 battery groups, and allows more amps to flow when the voltage difference is greater. Once the difference is around 0.4V (or less), the echo-charger stops charging.

After a couple of weeks not plugged in, your house battery will slowly drain, as the newer coaches have more permanent loads.
The chassis battery should remain at a higer level much longer, as the only load on it is the security alarm (at least on my older coach).

Henk Bots, 2000 Magna 5824.

Re: Battery state of charge

Reply #4 –
Yahoo Message Number: 21273
R.D.

Just a couple of thoughts that may be of some help:
- What others have posted is correct... your batteries SHOULD show a higher voltage while the charger is on (13.8 sounds normal) and lower when the charger is off (12.7 would be fully charged with no drains/loads).

- What is the ambient temperature where you are? The "resting voltage" of a fully charged battery (that has been charged fully and now has not voltage and/or loads applied to it) is 12.7V at 80 degrees
F. If the battery is colder than that, the resting voltage will drop.
If it is warmer, it will rise. So, if it's cold where you are, that will have an effect.

- I'm not 100% sure how the electrical system is configured in your coach, but if the Xantrex is responsible for charging the house batteries, look in the manual to figure out how to check the setting for the TYPE of battery you have it charging. AGMs require a different charging profile than "wet" batteries. The Xantrex should have a setting for this. If it is set for "flooded" or "Gel Cell" charging, it's possible that it has damaged the AGMs (although the damage should be minimal since your coach is so new).
- AGM batteries do NOT need water... and you cannot open them to take specific gravity measurements with a hydrometer... so don't even try!
- Look at your coach batteries. There are probably more wires coming off of them than you would expect. While MOST of the house 12V loads are routed through the battery disconnect switch, on almost all RVs there are other items that are wired directly to the batteries. If this is the case, it's possible that one of those items is causing a fairly high drain/load on the batteries that is affecting your reading of the voltage when the charger is turned off. The only way to know for sure would be to fully charge the battery and then to disconnect all of the wires from it (make a thorough diagram and/or take a picture so you can get all of the wires hooked back up the right way), let it "rest" for about 4-6 hours and then take a reading. If it's still "low" (less than about 12.5), I'd take them in to a battery place and have them load test them. AGM's aren't cheap, so you want to be sure they're bad before replacing them (are they still under warranty?)

Hope this information is helpful!

- John

'05 Newmar MADP 4304 / Spartan MM GT / Cummins ISL 400hp '03 Honda CR-V toad

Quote from: R\. D\. Vanderslice
>

I've only been RV'ing 2 years and must confess that after reading
everything I can get my hands on, I'm still the ultimate electrical dummy. I marvel at you guys that spit out all these formulas, terminology, and knowledge of the electrical system on these coaches.
I'm a little concerned about my batteries state of charge. I've been home now from the East Coast rally about 5 weeks. My coach IS PLUGGED into 50 amp service, but has not been started up in those 5 weeks. I thought the chassis batteries probably were getting a little little low so I put the multi meter to them and they showed 13.3, which doesn't seem bad for 5 weeks, the house batteries show 13.8 These are two AGM batteries. The Sea Level Monitor on the bath wall shows the house batteries to be 13.8. The Xantrax panel shows 13.8, in float mode, and 100%. This is while PLUGGED into 50 amp service. All seems o.k. until I decided to check them while the coach is UNPLUGGED. I did this thinking that the battery charger
Quote
might be helping the three meters give a false reading. What I
found is that the chassis reading did not change (13.3) and that seems reasonable. However the house batteries now show 12.3 on the Sea Level Monitor, the Xantrax panel shows the "battery state of charge to be 78% of full", and the multi meter shows the house batteries to be at 12.2. I'm confused (that's not to abnormal for me) in that I thought that as long as you were plugged, in the house batteries should stay fully charged. I never thought to check them while unplugged and this caused me the confusion. Anyone out there have any thought on this? Are my two AGM house batteries being left in a state of low charge, thus possibly shortening their life?. Is my charging system maybe not fully charging my house batteries.? There is nothing on in the coach while parked except the Hydro Hot set at 50 degrees that occasionally comes on to prevent freezing, etc. Thanks.
 

Battery State of Charge

Reply #5 –
Yahoo Message Number: 21334
Hello Gang,

I just wanted to publicly thank Ned, Henk, John, and another John (siamese cats John), for their help is solving my battery charging issues. It appears I'm in good shape and now need to find something else to worry about.
This is a great group to learn from. The knowledge hears is amazing. I'm constantly learning from this group and the participants really have a knack for helping you without making you look like an idiot.

Thanks Again!!!!

R. D. Vanderslice
Rockwall, Texas

06 Allure 470, no. 31294