Ram Battery Low Voltage Warning

I dropped off the trailer in early April and the warnings have continued. I just got back from the dealer and the problem was a loose 250 amp fuse at the battery terminal. I don't know if the fuse itself was loose or whether the attachment to the battery post was loose. Anyway, no warnings on the way home.

The radio was also changing stations on its own and the service manager said that was probably related to the loose connection.

Sam Spade wrote:

wgriswold wrote:

Anyway I now think the problem is with the trailer and will test it when I get home and have more tools and time.

ALL of the voltages you report look perfectly normal.

You may need to contact a truck dealer to see what they know.
With the number and type of batteries that you have you might just have to live with that occasional indication.

Most all electrical systems that include a battery expect to HAVE a battery there....all the time. Voltages measured without a battery in the circuit can be deceiving unless you have some engineering spec's to tell you what to expect.

I am leaning toward a bad connection to the trailer. The 7 pin cord is 15 years old and I will replace it and see what develops.

Thanks for your help.

wgriswold wrote:

Anyway I now think the problem is with the trailer and will test it when I get home and have more tools and time.

ALL of the voltages you report look perfectly normal.

You may need to contact a truck dealer to see what they know.
With the number and type of batteries that you have you might just have to live with that occasional indication.

Most all electrical systems that include a battery expect to HAVE a battery there....all the time. Voltages measured without a battery in the circuit can be deceiving unless you have some engineering spec's to tell you what to expect.

Sam Spade wrote:

wgriswold wrote:

Yes, done that. The truck was 12.6V resting and 14.3 running. The trailer was 12.6V not connected to the truck.

And only reported half the results.
I said to test BOTH sets of batteries in BOTH situations.

So....what did the trailer battery read when connected to the running truck? And what did the truck battery read at the same time.....or a few seconds later ??

And a P.S. after reading another post of yours:
Measuring the voltage on the battery cables while they ARE NOT CONNECTED TO THE BATTERY proves pretty much nothing.

And now I have forgotten what the original question was.

o....what did the trailer battery read when connected to the running truck? --14.3V

And what did the truck battery read at the same time --14.3V

Measuring the voltage on the battery cables while they ARE NOT CONNECTED TO THE BATTERY proves pretty much nothing.--My thought was to measure the charging voltage coming from the truck to the trailer batteries independent of the batteries. Analogous to measuring the output of he convertor.

Anyway I now think the problem is with the trailer and will test it when I get home and have more tools and time.

wgriswold wrote:

Yes, done that. The truck was 12.6V resting and 14.3 running. The trailer was 12.6V not connected to the truck.

And only reported half the results.
I said to test BOTH sets of batteries in BOTH situations.

So....what did the trailer battery read when connected to the running truck? And what did the truck battery read at the same time.....or a few seconds later ??

And a P.S. after reading another post of yours:
Measuring the voltage on the battery cables while they ARE NOT CONNECTED TO THE BATTERY proves pretty much nothing.

And now I have forgotten what the original question was.

If there is a warning about acid and tilting them, they are not AGM which can be mounted sideways...

I would load test all your batteries (truck and trailer) independently.

I just hooked the trailer up to the truck and took the wires off the trailer battery and measured 13.86V at the wires. So the truck is charging the batteries at an appropriate voltage.

The voltage at the batteries is 12.7V so they are charged. Perhaps one is bad and I will check the specific gravity of each cell when I get home.

wgriswold wrote:
I have one 220 amp alternator. I was told on another site that the batteries were AGM. I have confirmed that they are sealed maintenance free but not that they are AGM. The only thing on them that suggests their type is a warning about sulfuric acid and not to tip them. So I suspect that the guy on the other site was wrong and they are maintenance free lead acid batteries.

So the problem may be caused by something else in the trailer.

Did you make any modification to the charging system or wiring to setup the truck for charging the trailer batteries, or just using the factory 12v accessory line provided in the 7-way connector?

I was thinking, if you had installed a large gauge cable direct from the alternator to the trailer, the computer is sensing the voltage drop caused by the extra load (a load not programmed in) or it could be a ground loop or something else funny.

Like the previous poster pointed out, using factory connections, not much current flows, and it's fused. Likely that is programmed into the computer as a known load as well... so the battery voltage warning is coming from something other than the trailer connection.

I don't think that it's trailer related unless you did something to really discharge the truck (not running while connected to trailer)..

Connecting a running truck to an RV, current is going to be limited to 20-30 amps, max, before blowing a fuse. Your alternator can handle that easily.