400 battery not charging while towing with frig on DC

The biggy with the dc to dc charger is to make sure your wiring is heavy enough to support it.   Even though I have the DC to DC charger we still travel with the fridge on propane.

Not to dash your hopes, but we've found that our 2011 Toyota (Tacoma without factory tow package) is not affected by the 'headlights on', so I'd guess yours isn't either...

@Tundra57, have you tried any other means of supplementing your electrical system output, thus increasing the input to the battery?  Our former tv is a 2005 gmc Envoy xl. Like the chevy trailblazer, every vehicle had a full tow  pkg with 150 amp alternator and 10 guage charging line built in. While traveling the dessert southwest in 2016, we found even that vehicle was inadequate to keep the t@b battery charged while towing and running the fridge on 12v. We began looking for solutions and found something @Dalehelman devised. He made a set-up to attach his portable solar panel to his tv roof rack to charge the trailer battery as they traveled. We thought it was a brilliant and a near zero cost solution. My DH cut a piece of plywood to support our 80 watt solar suitcase and cut holes in the wood so it could be clamped to the luggage rack of our Envoy. Although not a large input, it was enough of a supplement to keep the t@b battery charged as we towed with the fridge on 12v. Now that we have the Chevy Silverado 2500 with a massive 220 amp alternator, which kicks into its full output and stays there in tow/haul mode, we kept the portable suitcase on the plywood, strapped it onto the top of the cargo in the truck bed, plugged it into the trailer, and kept our t@b battery literally at 100% charge all the time we traveled the Pacific Northwest (more than a month) this summer.  If you already have a portable solar panel, something to mount it to and hose clamps or even bungies, you could make something that would greatly improve the charging function into your trailer battery. We thank the master of modification, high professor of t@b university improvement and implementation department for his undeniable talent! @Dalehelman, we salute you.

Tundra57, I’ve been fighting this since buying my new Tacoma in July.  My last Tacoma, 2004, performed flawlessly.  I wired it myself.  Always charged whether trip was long or short.  I have the same problem as you with my new truck.  My 2019 is wired using the factory system.  I have tested my system fully.  I’m a retired Navy electronics tech so I know how to use meters.  Been down the headlight on, excite the alternator route, etc.  The voltages are correct but the amps are not enough to keep up with the refrigerator.  I have contacted two local dealer service departments.  There’re answer is they don’t know.  I contacted Toyota Corporate, they told me it wasn’t a thing they handle, and referred back to the dealer.  And this type problem is not isolated to Toyota’s.  I read about same problem on multiple late model vehicles.  So.... our options are:
1.   run a direct, heavier gage wire from truck battery with a fuse and relay using the factory plug charge line as the “on” for the relay and tap into the back of the truck 7way plug.
2.  Don’t run or expect our refrigerators to work as advertised connected to our vehicles.
3. Return to older tow vehicles which are less “tron” and sensor laden.
I’ll be performing #1, when I get around to it.

Actually, in the event of a break-away,  the break-away brakes are powered by the TaB battery, so you need to tow with the battery switch turned on.  

fridge draws 150w ac so as long as you use that or bigger should be ok. I use a 200w with a 400w spike capability

I thought the battery would be charged half as fast as the fridge draws power? I think that's what we were told when we bought the trailer??? 

We just turn the fridge on and off every other time we stop when we are driving. Checking the freezer temp with an indoor outdoor corded thermometer. Seems to keep battery charged and freezer doesn't get above 20 degrees.

Now you understand why the big three offered a heavy duty alternator for most vehicles in their line up for years.      In researching my replacement truck,  one of them offers an upgraded alternator as part of the tow  package.   Don't remember which one.

So 80 amps isn't going to go very far with the added trailer.    keep in mind that when you connect your TV to the trailer,   in addition too trying to run the fridge it is probably trying to charge the battery and power all of the various dc loads in the trailer,  might only add an amp or two but it still counts.

I am pretty sure towing after dark maxs out your alternator especially if running the blower motor for heat or ac.

I didn't bother to check but power bastards offers upgraded alternators for a large variety of vehicles,  they aren't cheap but worth a look and will more than likely solve your under powered alternator problem.

This discussion has me wondering if we could leave our fridge on DC while towing with our 2006 4Runner which has a 130 Amp alternator as far as I can tell? Will try that next time out.