Just how well do our Tundras charge the trailer batteries?

About to head south into two sub freezing nights boondocking at good old Cabelas parking lots. This will require the furnace to keep the water system from freezing and the blower requires about 8 amps when running. I know my battery is up to the chore each night but only if the + pin on the 7 pin will provide the same voltage that the charging system does. Big surprise that the opinions are all over the place on the web. Some say there is a blocking diode, some say it only trickle charges. Unless I get some good numbers from the experts here I'll be taking some readings of my own during the trip outta the cold weather. TV is a 21 with tow package.

 

Ive heard that it trickle charges, but I dont know how true that is.

If you do a lot of boondocking look into the Goal Zero Battery generator. There are a few similar models.

Also look into the propane heaters. I can run for weeks of a 20 gallon propane tank. Plus you can cook on it, heat small spaces, its portable and propane is available at most gas stations, hardware stores. Just a thought. Im looking forward to boon docking in the teens here shortly!

 

Considering that the Tundra shuts off it's USB ports when you turn off the engine, I wouldn't be holding out any great hope that the trailer plug gets any more charge than zero when it's off.

 

I'm hoping it does shut off with the key. Draining the truck battery would ruin my day. I'm only concerned how much the Tundra's system can recharge my trailer battery while driving down the road during the day.

 

Ah, I misunderstood then.

Can you just voltmeter the plug on the truck after identifying the battery pin? Or hook up and volt meter the batter to see how much the charge goes up?

 

You can simply measure for 12V at the 7 pin with key off with a multimeter or a test light to see if power is there constant or keyswitch. Most vehicles with a "tow package" and a 7 pin include the chassis side wiring for the power pin. I agree the internet search is dizzying on this topic when I tried to search it too. I added a solenoid to convert a Jeep Rubicon always hot 7th pin to a triggered source to only charge a camper trailer batter while driving. There was a couple of 30amp fuses under the hood if I'm remembering correctly so it seemed like it should handle a lot of current but the wire was tiny so there's really no way it was designed to. It would top off the camper battery on long drives only (~8-10 hrs), it was a lead acid so it was okay charge voltage. If your trailer has an AGM it won't 100% top off from factory Toyota charging system voltage.

FYI look closely, most 7 pin connection covers have a diagram of the pins on them.

 

As long as the battery in the trailer us drawing current from the Tundra I can tell. Just starting the truck and comparing no load voltages isn't going to tell me much. If my battery cover doesn't have two small meter probe holes in the cover it will today. I doubt the battery charge indicator in the trailer is of any real quality to be useful. My trusty Fluke poked into the test holes first thing the next morning after spending a night on battery compared to end of travel day should give me what I need especially if I can test while the furnace is running. Just wondering if anyone had already experienced this situation.

 

This is the main reason to put some Solar on your Camper!
That way you have a constant source of charging current regardless of the the trucks output to the trailer.

Otherwise,You would need to run the Ammeter on a Fluke to understand the charging Current delivered to the trailer from the truck not the Voltage and you will need a Meter that can handle readings in the more than 10amp range in the chance that you are getting that much from the truck which I kind of doubt but honestly do not know for sure either. Many Meters will only read up to 10amps of current without a Shunt in circuit with them.

I cant believe I am saying this but I would ask several RV dealers Service Departments first just to see what kind of answers you get while taking the answers with a huge grain of salt at the same time!

Also I have an advanced battery monitor in my Trailers and you do too you could just see where you are there when starting off and then after a longish drive and see if the battery is being charged and at what level from there.
The Battery Monitors will have current shunts built in to be able to measure the high current from the truck without letting smoke out of the Monitor like you might with a low current reading meter too!

 

I run with this guy

 

Testing a battery charger off under load can give you a very accurate indication of the battery condition. RR Xing lights and gates have backup batteries and are tested monthly both AC power on and off under a load to test battery state of charge.

 

My experience towing my camper is the truck charges it VERY slowly. We have two batteries and a 100w portable solar panel that keep them topped off

 

Thank you for your input. I'm debating on taking a small generator with us just in case. Problem is it's the same one that I use at the house to keep the deep freeze and fridge cold when the power goes out. My neighbor is watching over the place while away and don't want to remove that option from him.

 

I just tried a quick experiment. Trailer is connected to shore power with furnace on the voltage was lower than I'd prefer at 13.12. This isn't a temp compensation charger in the trailer. Unplug AC and let sit for 30 minutes with furnace running at least most of the time. Voltage was 12.15. Back the Tundra to the trailer and plug in the 7 pin. By the time I got the Fluke on the battery ( five-ten seconds?) voltage was 13.31 and climbing. Unplug the truck and plug in shore power I read 13.52. I do have a much better charger packed away with a temp probe that I'm going to change once I get to a warmer clime.

 

What are you looking to power in the camper?

 

I can confirm that the 7way is switched with the ignition. I can also confirm that it supplies vehicle running voltage when unloaded. 13v @ 0 amps?

The people over at etrailer are knowledgeable. This question has been asked over there a dozen ways. The concensus is that the 7 way provides a maintenance trickle at best.

https://www.etrailer.com/question-226997.html

 

I'm only concerned about a few LED lights, the furnace and whatever the fridge requires while on LP. Maybe charge phones on the USB port. If below freezing a small power supply fan that uses 80 ma to blow warmish air into the water tank compartment under the bed. Turns out the Gulfstream trailers made with Adzel are fairly well insulated so after heating up the inside and everything in it, it seldom runs.

 

Maybe pick up one of these for peace of mind. I’ve been very impressed with mine.
Mr. Heater F232000 MH9BX Buddy 4,000-9,000-BTU Indoor-Safe Portable Propane Radiant Heater, Red-Black

$78 Mr. Heater Portable Buddy Heater MH9BX 4000-9000 BTU Indoor-Safe Propane Radiant Heater For Campers, Workshops, Job Sites, Patios & More - Red, Black

https://www.amazon.com/dp/B002G51BZU

 

My good neighbor offered one to me but due to the dog sharing space and that we need to keep warm air circulation around the plumbing, we declined. We like a cold bedroom too. The lowest forecast temp is 26 degrees and this will be right before dawn. I'll have been up with coffee in hand and chomping at the bit to hit Paneras for bagels way before the sun comes up.

On a side note it's challenging for my wife to understand we had to get a stove top percolator coffee pot since her little one cup Keurig will be nothing more than taking up space on the counter.

 

That’s exactly what we use. Got the solar panel and all the connectors and wire for under $200. With the two batteries we never run out of juice

 

Can you explain this a bit more or direct me to a thread that does? I've noticed my second battery, and even my primary, arent reaching full voltage like my old factory battery did.

Thanks,
Gavin

 

Toyota has their alternator only put out 13.0-13.5v. AGMs require 14+ to recharge properly. You can change the alt-s fuse to trick the computer into giving around 14v. Search Toyota alternator diode or voltage booster.

 

Roger that, thank you!

 

$14 Littelfuse 02400104P 1A Mini Diode Automotive Fuse-4Pack

https://www.amazon.com/dp/B015YSU24G/?coliid=I3KL59QTZY88E2&colid=3313QK6L78XGN&ref_=lv_ov_lig_dp_it

 

A quick report back on the battery status after our trip down. Had no problems running the furnace all night and intermittent use of lights, the water pump, fridge and LP water heater all night and charging back the next day driving. I believe the Tundra charges much better than a trickle charge.

 

I've always been told that it's not more than a trickle charge, but according to the (not super accurate) battery charge indicator on my trailer, it seems to top it off without much driving. Glad it worked out for you.