battery doesn't seem to be charging while driving

northwestinatab · June 2019

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!
Northwestinatab

pthomas745 · June 2019

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.

https://www.solar-electric.com/learning-center/batteries-and-charging/deep-cycle-battery-faq.html#Battery Voltages

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

ChanW · June 2019

Another point, disconnect from the tow vehicle to 'rest' the battery and make those measurements. Your TV battery could be affecting your readings...

Sharon_is_SAM · June 2019

@northwestinatab,

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?

rkj__ · June 2019

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.

Cbusguy · June 2019

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.

ScottG · June 2019

@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!

northwestinatab · June 2019

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...

THANK YOU.
Northwestinatab...

pthomas745 · June 2019

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.

dsfdogs · June 2019

One more point...the battery switch needs to be ON while towing or anytime you want to charge the battery.

davel4wa · June 2019

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.

northwestinatab · June 2019

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!

2Cougs · June 2019

@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.

GrandmasKid · October 2019

Finally I've figured out that my TV is not charging my RV battery at all. I'm a little slow but I really want to get the charge line to work. My charge line comes from the starter battery in my TV. My circuit tester tells that voltage is getting to my seven pin receptacle on the TV. From there does the charge go to the positive pole of my RV battery? Is it possible that the charging wire is connected to the wrong side of my RV battery? If the charge goes directly to my RV battery maybe I should pull some wires off the RV battery and see if a line with current is attached to the negative pole. If I do this perhaps I should have my wife watching and ready to perform CPR after calling 911. Any advice is greatly appreciated. One thing I don't get (OK maybe more than one thing) is the test that Sharon above suggested. When I connect my charging line to the T@B with the cutoff in the off position (RV battery not connected to the RV) of course the inside light won't come on if the charge line goes to the battery, right? Does the current from the TV go to a controller before it goes to the RV battery? I'm so confused. I need a hug.

Sharon_is_SAM · October 2019

@GrandmasKid - First a hug .🤗

The 7 pin carries voltage from your TV to the junction box under the front of the TaB. The battery positive terminal connects to the cut off switch which connects at the junction box. The negative battery terminal connects at the junction box. The junction box and TaB 7 pin is pre-wired at the factory. The dealer connects the battery.

If you connect your 7 pin with the battery switch off, if you have a charge line that is transmitting adequate voltage, you should be able to turn on an interior light in the TaB. I would take a look at your 7 pin and make sure a pin is not bent or corroded, then I would look in the junction box and see if something is loose. I would also trace the battery lines to the junction box to see where they run. Is the cut off switch on your positive terminal?

MuttonChops · October 2019

@GrandmasKid
Below are two diagrams that might help your "see" how things are connected.

First, 7-Pin Wiring.
Note: Sometimes aftermarket +12V wires from the TV Battery are connected to the Trailer Backup Light pin. Confirm your +12V is on the correct " +12V " Pin and not the back-up pin.

Image: https://us.v-cdn.net/5021717/uploads/editor/z3/5iiz7dk2yyh9.png

Second, Junction Box (on frame under front tub) wiring.
Note: As stated by others normally the Battery Cut-Off Switch is placed on the Battery Positive Wire between the Junction box and Battery.

{ edited figure to Show Cut-Off Switch }
{ 10-16-2019 }

Image: https://us.v-cdn.net/5021717/uploads/editor/p7/zqw9fgkufbz4.png

ChanW · October 2019

Yes @GrandmasKid, using your voltmeter/multimeter, the TV 12v should show on the battery cables, with the battery disconnected, and the cutoff switch on. The reason it would also light the interior light is because the junction box splits the 12v line out to go to the Tab convertor.

No need to worry about shock, if your hands are dry (and you don't short the cables together!)

If the 12v doesn't show on the battery cables, then go back a step and get under the tongue and take the cover off the junction box. Look for corrosion there, it's sometimes not sealed thoroughly against road splash. Also check the connections on the cutoff switch for corrosion or looseness.

You can test each of these connections with the voltmeter before disconnecting/ cleaning connections to see if you're getting power to that point.

GrandmasKid · October 2019

Thank all of you for your help. I've traced the current back through the other side of the controller and it is very weak. The junction box is clean without any corrosion and the nuts are tight. The voltage is so weak it barely turns on my circuit tester light. I don't know much about this and have more questions that probably are pretty dumb but here goes. My charge line comes from my TV battery. Is that where it should come from or should it come directly from the alternator? Perhaps my TV (a 2010 Toyota Highlander Hybrid) has an alternator that just can't keep up with the amps that I need to run my Norcold refrigerator in the T@B while driving. I keep thinking maybe I'll buy a multimeter even though it seems a shame to spend the money for something I'll probably use once in my life to tell me something I already suspect. I like my TV for its ride, cargo capacity, and high mpg, so I don't think I'll be trading it in anytime soon. Maybe I should put a flexible solar panel on the roof, or use a battery booster of some sort. Are there any other suggestions for how to handle my problem? Again, thank you very much for your help.

JEB · October 2019

GrandmasKid said:

Thank all of you for your help. I've traced the current back through the other side of the controller and it is very weak. The junction box is clean without any corrosion and the nuts are tight. The voltage is so weak it barely turns on my circuit tester light. I don't know much about this and have more questions that probably are pretty dumb but here goes. My charge line comes from my TV battery. Is that where it should come from or should it come directly from the alternator? Perhaps my TV (a 2010 Toyota Highlander Hybrid) has an alternator that just can't keep up with the amps that I need to run my Norcold refrigerator in the T@B while driving. I keep thinking maybe I'll buy a multimeter even though it seems a shame to spend the money for something I'll probably use once in my life to tell me something I already suspect. I like my TV for its ride, cargo capacity, and high mpg, so I don't think I'll be trading it in anytime soon. Maybe I should put a flexible solar panel on the roof, or use a battery booster of some sort. Are there any other suggestions for how to handle my problem? Again, thank you very much for your help.

I hadn’t previously considered the kind of tow vehicle you had. Hybrids ordinarily don’t make good tow vehicles. At least not yet. The electrical systems are designed to devote most of the electrical production to recharging the main battery banks used to propel the vehicle. Toyota’s hybrids have small alternators and small starting batteries because bigger ones generally aren’t needed. You’re problem might be systemic because it simply isn’t designed to charge externally. I’d be reluctant to try to tie into the main generators used to recharge the lithium bank because I’m not sure you’d want to take energy away from that process. I’d recommend talking to someone who is an expert in hybrid systems.

GatorEgg · October 2019

I’ve been troubleshooting this same condition on my 2019 Tacoma. Verified good- batteries, 12vdc on truck plug. I’ve contacted for electrical numbers - Toyota, Norcold(refrigerator) and Nucamp dealer. Norcold 3way refrig pulls 11.3 amps per parent company Theford. Toyota Corporate techs don’t know how many amps are provided at charge line pin on truck 7 way plug. Referred me to an “Rv repair place” or Toyota dealer. Toyota dealer “doesn’t know” referred me to a “Rv repair place”, or trailer dealer. Nucamp dealer says that’s a truck dealer question. Which it should be. Beginning of week I plan on dropping by a couple local Toyota dealers firsthand.

Sharon_is_SAM · October 2019

@GrandmasKid, I would inquire if it is possible to change your charge line to 8 or 10 gauge and if so, will that reduce voltage drop and increase your current. Or, it may not have anything to do with voltage drop as JEB suggested.

Cbusguy · October 2019

@GatorEgg a quick and dirty way to trouble shoot would be to use a set of jumper cables from the truck to the trailer. Using an amprobe or amp meter, have a helper rev the truck engine to normal road rpms and see what sort of amps are delivered. Might try the headlights on off trick as well.

This would tell you if the limiting factor is wiring, or alternator.

That 7 pin connector isn't designed for sustained high amperage, so I bypassed it.

ChanW · October 2019

@GrandmasKid & @GatorEgg, I had the same question on our Tacoma, whether or not it could keep up with the 3-way fridge, as it didn't seem to be doing it very well. I finally got the answer once our Victron battery monitor was operational, because it was showing me the actual amperage going into the battery at all times.

It turns out our Tacoma alternator is not putting out enough to keep the 3-way fridge going on 12V mode. The battery monitor showed that the alternator was putting out high current only shortly after starting but that it reduces pretty quickly to a 'trickle charge'. I also checked to see if there was a difference with the TV headlights on, as some have suggested, but it showed no difference in output power.

Note that I have the standard alternator and not the tow package.

I have a number 8 or 10 gauge wire going directly from the TV's battery/alternator cable to the 7-pin. It should probably be heavier-duty, maybe number 6, but I don't think it would help.

The one thing you have to keep in mind is that the alternator is sensing the charge of the battery, and the charge on the TV battery (closer) is probably going to supersede the charge on the Tab battery. But also the charge algorithm on the TV alternator is intended to specifically support the starter battery (on mine anyway), which normally doesn't do much more demanding than crank over the engine here and there.

@GrandmasKid, with a hybrid, keep in mind that your alternator is designed to charge a lithium battery bank, as opposed to the lead acid type of battery in the Tab. It seems there's a good possibility it wouldn't charge the Tab correctly at all.

Also, re using solar... I've found that having the solar charging while on the road helps recharge from the night before discharged state. But you would have to have a pretty good-sized solar panel set up, in order to keep up with the three-way fridge's current demands. Not really practical, I think.

Just my layman's thoughts...

GrandmasKid · October 2019

There is something I'm missing. I tow with a Highlander Hybrid. I think its alternator charges the big NiMH batteries and the standard lead acid starter battery. My RV charge line comes off of the starter battery. Since the TV starter battery doesn't seem depleted after a long day of towing, and all the connections in the charge line all the way through to the T@B battery seem fine, it's a mystery to me as to why my T@B is not getting charged while towing.

As for charging once we get into camp, the Zamp 160 watts of solar has no trouble charging our 92Ah, AMG battery all the way up even if we don't have full sun. After eleven hours on the road and pulling into the Shenandoah Mountains we still had enough juice to run the fridge on propane until we could solar charge the next day. Maybe I worry too much but I think I'll buy an emergency battery charger just in case. As always I'm grateful for all the comments and suggestions found in this wonderful forum.

JEB · October 2019

GrandmasKid said:

There is something I'm missing. I tow with a Highlander Hybrid. I think its alternator charges the big NiMH batteries and the standard lead acid starter battery. My RV charge line comes off of the starter battery. Since the TV starter battery doesn't seem depleted after a long day of towing, and all the connections in the charge line all the way through to the T@B battery seem fine, it's a mystery to me as to why my T@B is not getting charged while towing.

I used to own a Prius. I could be wrong about this, but I don’t think the alternator that recharges the starter battery is the same “generator” that recharges the lithium (NiMH?) bank. As I said previously, I think the charging systems are separate in Toyota’s hybrid systems and the part that charges the starter battery is smaller and less robust. I urge you to talk to a hybrid expert on this.

GrandmasKid · October 2019

Well now I'm frustrated. I bought a multimeter to try to get things figured out. I hooked everything up and the lights and turn signals worked. I turned everything off and started following voltages and tried measuring amps of the charge line which barely registered. Hooked up and turned on and now the lights won't turn on and the brakes won't connect. Now I can't even tow it to a professional without risking a ticket or an accident. Are there fuses inside the Prodigy controller that might have blown? Any suggestions will be greatly appreciated. Wait! Happy days are here again! I found a lose wire in the 4pin flat to 7 blade adapter. I still haven't figured out why my tow vehicle can't charge the camper battery, but at least I can tow legally. Apparently the trailer brakes work without the TV battery connected. Can anyone tell me if the breakaway function will work without the trailer battery connected to the camper? I'm considering towing while using the cutoff switch to isolate the battery from the camper since the lights and brakes are working with the camper battery isolated.

gulfarea · October 2019

Brakaway works with the trailer battery, Art

Verna · October 2019

@GrandmasKid, you need a 7 pin connector on your tow vehicle to have a path for the charging line to go From your Highlander’s battery to your T@B’s battery to charge it while towing. A 4- pin connector only gives you turn signal, parking and brake lights. That is why your Highlander cannot charge your T@B’s battery while towing.

GrandmasKid · October 2019

If anyone can set me straight on this I'd appreciate it. My TV alternator charges the car starter battery. I see that that battery reads 14v measured at the battery after the car has been running a little while. The charge line is connected to the starter battery, not the alternator. So the TV alternator's job in part is to keep the starter battery charged up, which it has no apparent trouble doing, even when towing my T@B with the refrigerator running. However, the camper deep cycle 92 amph AGM battery has gotten down to about 35% after a day of towing. My question is, if the TV alternator is keeping up with the starter battery, why isn't the camper battery getting charged? The camper battery is apparently not getting charged even with with the refrigerator off.

Verna · October 2019

@GrandmasKid, please read my post.....it above your latest post.

GrandmasKid · October 2019

I have a seperate charge line from the TV starter battery to the rear of the car that comes out next to the 4 pin flat receptacle. From there the charge line connects to an adapter for the seven blade adapter. I'm in the process of following that further but I need some aligator clip leads that should be here in a couple of days. Maybe there's a fault on the adapter. I should know soon. Thanks for your help.

battery doesn't seem to be charging while driving

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