battery doesn't seem to be charging while driving

Hi there,

You guys are very helpful so hoping can be with this issue too.. First a long explanation but if want to skip and go to question, it is at the end... 

On the road and driving about 4-5 hours per day, and somehow discharged battery down to 11.1.  Took to O'Reilly to get checked and it registered "bad battery" so I bought a new one.  Superstart 24 dcmj with 2/19 date on sticker, meaning it sat on their shelf since Feb.  Did not ask the guy to check it before putting in the tub (too big of a hurry to get to next town.  :-(  Also too newbie to know I should have at least checked battery level on Seelevel with my truck turned off.  Instead, I turned on the truck and checked the See level which said 12.9.  The guy said it was probably low from sitting on shelf and should "charge right up" with the truck.  I agreed and drove away.  5 hours later get to next campsite and check seelevel without the truck connected (and no shore power), and it says 12.7!  Since last check was with truck running, not sure if it actually lost charge or was just lower than that when I left the battery place.  Either way, now I'm concerned I've got another battery issue....

Now, in both cases, old and new battery, when hooked to shore power, battery says 13.6.  So it charges up on shore power, but doesn't appear to charge up on the truck battery while driving, nor did the old one hold a charge.  The new one will get checked in the morning....

When driving, I turn the fridge OFF rather than on battery because I was putting it on "battery" or just leaving it on electric before, and I think that might be what drained down the first battery....  

So the QUESTION is, shouldn't my truck be charging the battery while I drive down the road?  And, shouldn't the battery reading be the same whether connected or not, if it is holding a charge?

Thanks for help!


  • pthomas745pthomas745 Posts: 881Member
    A change from 12.9 to 12.7 doesn't really tell you much.  It is still at roughly 100 percent state of charge. 13.6 is also a normal reading while a battery is being charged, but it still doesn't tell you much.

    A battery needs to be "rested" before you can make any determination about state of charge.  You need to turn everything off and let it sit for an hour or so.  (Sounds healthy to me, though.)

    In this FAQ, there is a section on battery charging and "False Capacity" which explains the whole idea of getting the state of charge from a rested battery.

    Not every vehicle charges while driving down the road.  My VW Touareg does not.

  • ChanWChanW Posts: 2,332Member
    Another point, disconnect from the tow vehicle to 'rest' the battery and make those measurements. Your TV battery could be affecting your readings...
    Chan       --         Buffalo NY (Beau Fleuve)
    2014 'S' Maxx - 2011 Tacoma 4cyl Access Cab
  • Sharon_is_SAMSharon_is_SAM Posts: 4,474Moderator
    edited June 1

    I think we need more info.  Are you certain that you have a charge line?  (See below). Have you ever confirmed that the TV actually charged the TaB battery?  

    The easiest way to tell if you have a charge line without using any meters. (This method does not tell you how efficient it is).  
    Turn off your TaB battery by turning off the battery cutoff switch.  Hook your TaB to the 7-pin, crank the TV engine. Turn on an interior light in the TaB.  If it comes on, you have a charge line. Turn off the engine, if the light goes out, you have an isolation relay in your TV and your ignition controls the output from the TV battery.  If the light stays on, you do not have an isolation relay and your 7 pin connection from the TV is always live (can potentially drain the TV battery).

    The 13.6 v reflects the output of the converter.  To determine the state of charge, turn off everything possible in the trailer,  disconnect from shore power (and the truck), rest the battery, then check the SeeLevel.  

    Another thought, is it possible the 7 pin was not connected completely while towing?

    Sharon / 2017 [email protected] CSS / 2015 Toyota Sienna Minivan / Cleveland Heights, Ohio
  • rkj__rkj__ Posts: 593Member
    Last time I had an issue with my vehicle charging my trailer battery, I checked both the trailer connection and vehicle connection with a multimeter, and found both to be good. I eventually concluded that it was simply the connection between the two plugs. I cleaned the contacts, and it worked fine. 

    In some trucks, you need to add a fuse in the fuse box to make the trailer charge line live. In some vehicles, there may not be wiring run to the charge pun of the connector, and you will need to add it. 

    A full battery will read 12.6+ 

    A charging battery should read between 13.5 and 14V typically. 
    2016 [email protected] 320 CS-S - 2018 GMC Sierra - St. Catharines, Ontario, Canada
  • CbusguyCbusguy Posts: 438Member
    I agree with the above,  either the Tow Vehicle isn't wired to charge the trailer or their is an issue with the associated wiring and connection.

    A parting thought,   a number of Ford vehicles have marginally capable electrical systems,   batterys and alternators that it is possible that the additional load cannot be supported by the vehicle.    
    2009 GMC Canyon,   3.7 liter with added tranny coolerPower Bastards 250 amp alternator , added 2 gage charging wire to Trailer,  Timbren SES suspension and Super Springs.
    2020 320s Boondock lite, With Lots of mods
  • ScottGScottG Posts: 3,113Moderator
    edited June 1
    @northwestinatab, to emphasize what others have said--and what you already may have figured out given your own assessment of the situation--the SeaLevel reading is not necessarily telling you the voltage of the battery. If there is any charging input to the battery (converter, tow vehicle generator/alternator, solar panel, etc.) than what you see on the display is the charging voltage.
    The battery needs to be disconnected from any charging source--and from any load--and allowed to rest before it will reflect an accurate voltage. Ideally, that voltage should be checked at the battery itself with a reliable meter.
    That said, even with a marginal charging system on your tow vehicle, I would have expected to see a surface charge of >12.7V immediately upon disconnecting. Your observations suggest that your new battery is fine, but your truck is not charging it as you drive.
    Now that you are hooked up to shore power and clearly getting a charge of 13.6V from the converter, you'll know soon enough if the battery is taking a charge as it should. Just remember, you need to disconnect the battery and let the surface charge dissipate (which can take several hours) to get a true reading.
    Do the same with your original battery. As you suggested, you probably drained it by using the fridge on battery power. Deep cycling it to 11.1V may have compromised it somewhat, but I suspect it still has some usable life left in it. Good luck!
  • northwestinatabnorthwestinatab Posts: 20Member
    As usual, you guys have been incredibly helpful!  I've read the link sent in first post and learned a lot from that, then reading the remaining posts made sense and I'm going to do the tests recommended.  Planning to camp without hookups for a couple of days and although I have solar panels, suspect I will be learning rather quickly what to do and not do.  I thought about skipping that camp reservation and staying at full hookup place while I learn, but only going to be near the Sequoias once -- this year -- so going to take advantage of it.  Your helpful advice and information is going to make it easier.  I will post again after that and running the tests and let you know what I turned up.  My TV is a Toyota Tacoma btw...


  • pthomas745pthomas745 Posts: 881Member
    Yes, the Sequoias are worth risking a battery!  But, I bet you do fine.  Hint:  get up before the sun is really up and wander through Congress Grove before all those "people" get there.

  • dsfdogsdsfdogs Posts: 325Member
    One more point...the battery switch needs to be ON while towing or anytime you want to charge the battery.
    Debbie in Oregon
    2018 [email protected] 320 S/2019 Toyota 4Runner SR5
  • davel4wadavel4wa Posts: 88Member
    People checking your battery, including the AAA folks, are trying to sell a battery. You cannot assess a battery's capacity without first charging the battery. If your battery is already depleted and you load test it the result will be obvious. If your battery was at 11.1 volts it would probably take several hours to recharge it to it's normal charge level. Load testing after charging would produce an accurate result. Deep cycle batteries that are used in RVs are designed to be discharged repeatedly without seriously affecting their performance. Obviously discharging them to that level repeatedly will affect the life of the battery. I mention AAA here because I had an experience where I managed to accidentally defeat the auto off feature on my car while parked at work and the AAA tech tested my battery and told me that it was bad. I told him to start my car and I would take my chances. I had that battery for another 4 years.
  • northwestinatabnorthwestinatab Posts: 20Member
    Hi again everyone,

    I'm writing with an update.  First, I stayed in Sentinel Campground in King's Canyon and that drive through the King's Canyon River gorge -- while longish and a good 2 hours from the Giant Forest in the Sequoias -- is truly spectacular.  Second, I used my solar panels to keep the battery topped off, but didn't end up using much electricity in the camper, as everything has to be stored in the bear box and it was very cold outside (so no AC), so still have to experiment with that.  I did run the test recommended to see if I had a charge line from the truck, and I do, and it is controlled by the ignition.  So I've learned that much.  I so appreciate the advice I've received here as it allowed me to enjoy King's Canyon.  Thank you!

  • 2Cougs2Cougs Posts: 641Member
    @northwestinatab - Shhh!  You aren't supposed to tell anyone how wonderful King's Canyon is.  The rangers used to make us take an oath of silence ;)  Learned to fish rainbow trout there with my grandfather in the 60's.  Road down to Sentinel is quite the hill... but well worth it. 
    2016 [email protected] CS-S silver with white trim and WSU themed
    Pulled by a silver 2017 Chevy Silverado
    Leaves on [email protected] from Spokane, WA


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