truck battery dead after parking with trailer hooked up

[Gary Fowler]

I towed my Kubota to the dealer last week and when I came home I just left the trailer hooked up for the return trip. After 4-5 days of setting, I am going to go get my Kubota and my truck battery is completely dead. Not even the radio will work.
I jumped it off and it charged back up on the 20 mile trip to town but voltmeter was reading above 14 volts all the way to dealer and then half way back it dropped back below 14v so I assume it took about 50 miles of driving to recharge the 5+ year old battery completely.
What would make the trailer pull down my truck battery. Nothing should have been on except the power to the breakaway battery pack.
IS THIS NORMAL FOR ELECTRIC BRAKES?

[Mickey_Fx]

Don't have enough info to be sure of anything. Think you need to use a multi-meter and look for current flow when the setup is "off". It's possible your brake controller is applying some power to the brakes. Next, if you find the controller is applying some power, you need to find out if that is normal for the controller you have or do you have a problem.

[s219]

I've left mine hooked up for a week with no issues. Makes me thing something is wrong with your controller or wiring.

[Car Doc]

If the battery in the trailer brake battery pack is bad it will suck the life out of the truck battery. I may be wrong but I thought there were diodes or something like a relay box available to stop the charging or drain of a trailer battery like campers use?

[Gary Fowler]

The trailer is less than 6 months old as well as the controller so I dont know what it could be. I dont think there is power to the controller when switch is off, but the power to the trailer battery might be live at all times, I will have to check that and see. I have never opened the container for the battery to look at it.
Any othe rsuggestions?

[joshuabardwell]

Here is how I would troubleshoot this. Disconnect the negative lead from your battery's post, then set your multimeter up to read DC amps. Most multimeters will have like a 10-amp and a milliamp range. Use the 10-amp range at first. Put the multimeter in-line inbetween your battery's negative post and the negative lead. See if you have any current flowing. If you see less than about 250 mA, switch the multimeter to the milliamp range because it will give better precision. Generally, the "background" current in a vehicle with the ignition off should be in the milliamps range--maybe less than 20 mA or so. If you see significant current flow, you have "parasitic load" that is draining your battery.

If you have parasitic load, the next thing to do is to figure out where it is coming from. The first thing I would do is disconnect the trailer and re-measure. After that, start pulling fuses from your fuse box one at a time. When the current drain goes away, you've identified the circuit that is causing the drain.

Assuming you have a charging circuit hooked up to your trailer brake controller, your brake controller's battery is going to be able to draw from your truck's electrical system. If your brake controller's battery is damaged, it will be perpetually at low voltage, and will constantly drain your truck's battery down to its level. But I'm skeptical of this diagnosis, because I am under the impression that the trailer electrical harness is turned off in the truck when the ignition is removed, so the trailer battery would only be "pulling" when the truck was on, and then it would be supported by the alternator, so it wouldn't drain your battery. Nevertheless, a multimeter on the negative post of the battery will tell the tale.

[jwstewar]

, because I am under the impression that the trailer electrical harness is turned off in the truck when the ignition is removed, so the trailer battery would only be "pulling" when the truck was on

Not all vehicles do. I believe Ford & Dodge do, but GM doesn't - or at least didn't at recently as 2008. Our 2008 Suburban and 1999 Silverado are hot all the time.

[joshuabardwell]

Not all vehicles do. I believe Ford & Dodge do, but GM doesn't - or at least didn't at recently as 2008. Our 2008 Suburban and 1999 Silverado are hot all the time.

Seems kind of dumb to me, but what do I know?

[Willl]

Our 2008 Suburban and 1999 Silverado are hot all the time.

Which wire stays hot ?

Do you have a separate wire to charge batt ?

[Gary Fowler]

I pulled up the wiring schematic on 7 pin connection and checked the one labeled aux power on the truck and it is hot all the time so I know what drained the battery. Question now is why. Tomorrow I plan to open the battery box on the trailer and check the battery. I wouldnt think it would be bad this quick. The trailer was bought new in May of this year. It did set for several months without any use or power.
Any one have suggestion on how to keep these little batteries charged.