bunk heater

Mine doesn't shut off, you may have an alternator issue. Bunk heater draws very little current.

 

Webasto and Espar use very little power. I can run my cooler and heater for most of a day befor the low voltage warning comes on. And that's with 7 year old batteries.

A Pro Heat X-45 will kill four strong batteries in 10 hours but you'll get warm coolant too.

I'd say you have a battery/ charging problem

 

How many volts showing going down the road?

You could have a parasitic drain that you're not aware of.

If you're getting up 4 times a night, that's every 2 hours. How long do you let it run for?

 

Why did you change the batteries? Did you have them tested prior to replacing them?

Were they not holding/accepting a charge?

Do you have lights in the under bunk storage that are possibly not shutting off?

 

If you are showing almost 15v when it is running, you may have a voltage regulator that is stuck wide open, cooking your batteries. Or there may be a short somewhere, and the charge is not making it to the batteries.

 

He's right, 15v is too much if its constant.

After driving for a while, shut it off and check the voltmeter. Then run the heater for a few minutes and turn it off. Then check the voltmeter again.
This will tell you how much voltage you're starting off with.
This second reading will be more accurate than right after shutting the truck off because the batteries will have a "surface charge" immediately after charging.

 

High volts = low amps.