Battery Help?

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SantaCruzin

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Mar 12, 2020
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I'm at a bit of a loss for what could be going on with my batteries here.

One battery was just replaced (date code of 8/19) and one is from 6/17. I just bought the RV so can't say if they'd been run down regularly, but they seem to be in decent shape. I'm embarrassed to admit: I don't know which is the house battery and which is the battery for the engine. They are both in the engine bay and the wiring disappears into the bay and I can't obviously see which goes to the starter vs. back to the house.

Here's what's happening: When plugged into our garage outlet or a site the battery meter reads 13.4V and everything works as I'd expect. However, if the RV is unplugged from power for any time (need to test how long) the house battery is pretty much toast. The battery meter reads around 9V and I can't turn on any interior lights, start the generator, etc. I have to start the engine, then start the generator. Once I do this I can turn off the engine and the generator seems to keep everything running.

Do I have a drain somewhere? A bad battery? A misconnected circuit? A blown fuse?
 
If you really can't tell which battery is which remove the ground lead from one of them and turn the ignition to on - if you get no dash lights You've figured it out.

If you have a meter you can check the house current draw by (reconnect the ground) removing the positive cable and putting the meter between the positive terminal and the positive cable. Most decent meters should be able to read up to 10-15 amps.

If the house does not have an unusual draw then the battery may be too old to hold a charge. If the house is drawing anything over like 1/2 an amp dormant then something is drawing the current.
 
Odds are heavy it's a bad battery.  Get yourself a cheap VOM (voltmeter) at Harbor Freight and test the batteries directly. A fully charged 12v battery should read 12.6v or more with the shore power off (disconnected).  Or remove the ground (negative) cable to see what stops working - dash lights or house system.

https://www.harborfreight.com/7-function-digital-multimeter-63759.html
https://www.walmart.com/ip/Digital-Multimeter-with-Backlit-LCD-Display-and-Needle-Probes-Amp-Ohm-and-Voltage-Tester-for-Outlets-Wire-Continuity-and-Batteries-by-Stalwart/986468528
 
Thanks gents!

I have that exact Harbor Freight Voltmeter. It's been a little wonder of engineering...battery change aside it's been working well for 14 years!
 
YOu said one battery was recently replaced. clearly the chassis (engine) battery since it is good.

NOW: how to tell which Witch is Which.  Break out either a volt meter or a Automotive test lamp either will do for this...

With rig unplugged. generator off, measdure voltage battery terminal to battery terminal
One bright 12 or 13 volt range  CHASSIS.. one dim or dark or under 12 volts HOUSE

Both bright: You have a bad connection.
 
So, I've been tracking this over the weekend and I have a few update:

? The new battery is the house battery
? When plugged into power, the house battery reads 13.4V and the engine battery reads about 12.4V (assuming this means that being plugged into power charges the house battery, but not the engine battery)
? I tested to see if there was a draw on the house battery and could not detect one.
? I turned off everything in the house (I think) and unplugged power and the house battery read 12.4V, will check it again today to see if it has gone down at all.
 
Not good or bad, just observations:

13.4V is a very tepid trickle charge voltage.  Your battery will charge eventually at this voltage but it could take days to reach 100% if it is run down at all.

12.4V resting voltage is not fully charged.  I would plug it back in and let the tepid charger bring it up some more. 

If you want to check the box on getting a complete charge and not having to wait a week for it, replacing your converter with a contemporary multistage unit is on your checklist of things to do.

Mark B.
Albuquerque, NM



 
The 13.4 volts on the house battery indicates that a charge current is present. The chassis battery is indicating no charge current. This is probably the result of the charger not being designed to charge the chassis battery. That was a very common practice. If you will not be running the engine (which will charge the chassis and house battery) you can buy a battery cable and connect the two batteries temporarily so that the charger will charge both batteries while plugged in.

You mentioned you had loose wires in the battery compartment. Did you get those wires identified and safely fastened?
 
Henry J Fate said:
You mentioned you had loose wires in the battery compartment. Did you get those wires identified and safely fastened?
Click to expand...

Luckily, no loose wires for me! I couldn't see where some of them were routed, but I think I was able to track them all to verify they were connected.
 
You originally mentioned you didn't know which battery was the starter / chassis battery vs. your house / coach battery.

This may be silly but make sure your chassis battery is a starter battery and your house battery is a deep cycle battery. They look different which is why I brought it up. A starter battery won't perform well or last very long as a house battery.

 
Tom55555 said:
You originally mentioned you didn't know which battery was the starter / chassis battery vs. your house / coach battery.

This may be silly but make sure your chassis battery is a starter battery and your house battery is a deep cycle battery. They look different which is why I brought it up. A starter battery won't perform well or last very long as a house battery.
Click to expand...

Sometimes the housr battery is a "MARINE/deep cycle" and they look just like a common 12 volt starting battery.. Save for the label
 
Okay, some updates.
? Confirmed that the house battery date is 8/19 and is an AGM Marine/RV battery.
? I was busy with work and kiddos so didn't get a chance to check the battery voltage until yesterday (Thursday), but it is down to 9.2V. On Monday it was at 12.4V
? I reconnected the ohm meter and tried again to test for a draw. It's a bit finicky but I was able to get a reading that there WAS a draw of some sort, albeit a small one.

So, I think it's clear at this point that I have a draw and perhaps a bad battery. How would I go about tracking that down? I checked and everything appears to be turned off (lights, fridge, fans, water pump, water heater, etc.).
 
You need to use the amps (ammeter) function to measure a power draw - not the Ohms function (ohmeter). The charger should not be operating when measuring, so disconnect from shore power.
 
Buy a battery disconnect switch at an auto parts store and disconnect the battery when not being used. A small draw can be very hard to find in an RV and isn't likely something to worry about.
 
If the battery is at 9.2  volts and you still have a current draw, that would help some as most equipment would have shut down on low voltage. Lights, antenna clocks etc would continue to draw current. As Gary said earlier, make sure you are using the meter to measure current. The meter becomes the connection to the RV from the battery and all current being used will flow through the meter thus displaying the current in amps. Some meters do not offer that function.

A bad battery can shed a charge even if it is completly disconnected from any appliances or equipment.

A battery less than a year old can still be bad depending on the usage but since it is less than a year old,  charge it, take it out to Napa or one of the other auto parts places and have them put it on a tester to determine whether or not it is bad.
 
It sounds like the house battery is not getting fully charged. A battery at rest with 12.4 volts is fairly much discharged and it won't take long to draw it down further. If the battery is fully charged you should see 12.6 volts at least. Before you go replacing batteries I would let it charge for several days with no load and then check it again.
 
Just piling on here, there are a few different variables to isolate.  Phantom load, battery merit and converter status.  Address each one individually rather than try to use one to compare the other which can net you circular frustration.

Mark B.
Albuquerque, NM
 
Thanks all!

I ended up tracking down a battery shut-off (negative terminal disconnect) which I will likely use. I hooked up the RV to power today, and will let it charge for a few days to ensure the battery gets up to power. Once it is, I will disconnect the battery to see if it can hold a charge for any period of time.
 
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