battery problems

fishtait

I have a 2014 TAB Q Max and love it with the exception of ongoing battery issues. Here is the sequence: when I plug the battery into power, I register 13.8V. After charging for several days, when I unplug the system, I am usually at about 12.8V. But then, when I tow the trailer any distance (2+ hours) with the battery line connected to my truck, when I arrive the battery is at around 12.5V or lower. Is this normal? It means that I am already seriously depleted when I get to my bushwacking campsite. Is there something that I am missing? I have replaced the battery and still have the same kind of problems, and I have had the line from the truck tested to see if it is transmitting power. Thanks for any help you can give.

pthomas745

12.5 is not "seriously depleted." On a state of charge chart, that would be 90 percent of charge.  So, where did that 10 percent go?

What you are up against is the "false capacity" issue of a "non-rested" battery.

The 13.8v you are seeing while plugged in....is false...that is the charging current going to the battery.  All battery monitors of any type will display a value close to this when a battery is being charged.

The other side of the false reading of a charged battery is the false reading of a battery "in use."  If the trailer battery is "in use" when you are taking your reading...the voltage will always be lower than the actual voltage.  The parasitic drain of the trailer would be enough to have this happen.  Turn a few things on inside the trailer, and that "in use" reading will be even lower.

To rule out a failing battery...you need to take a battery voltage reading with the battery "at rest."  However you can disconnect the battery from the trailer: battery switch, pull the  fuse, or disconnect a battery cable.  Wait a little while, and then take a voltage reading. 

What are you using to monitor your battery and getting the voltage? The picture is from my Victron. Voltage reading on the left, the fan is running. Voltage 12.09, or 50 percent state of charge.  On the right, the trailer with the battery switch off ten minutes later, 12.46, or about 85 percent. 

Marceline

On top of what @pthomas745 says, if you are running your 3way fridge on DC mode on your way to the campsite, it's probably drawing down your battery because the power it consumes (10+amps) is greater than the output from your tow vehicle. But if you're at 12.5v you're not "seriously depleted." 

https://www.rvtechlibrary.com/images/voltchart.gif

Mellow_Yellow

Hi @fishtait - I also have a 2014. There is no built-in on/off switch, so when I'm not using the trailer, I pull the "30" amp fuse to ensure there is no passive drain on the battery. I also upgraded to a lithium ion battery and it seems to decharge much more slowly when boondocking, which is how I prefer to camp