APU and generator alternative that works!

Since I don't like the idea of dealing with gasoline generators and don't want to spend $14k on APU, I tried something different last summer with portable AC
Zerobreeze Mark 2 portable AC

That set up worked well for me and three of my friends who actually ended up using it more than me, since I took the July off.

Now comes winter time and my pre egr trucks have a hard time starting when it drops below 20 degrees and wouldn't start at all when it goes down to like 10.
Usually when it's below 20, I just always idle, however this year with fuel being very high, I needed to do something about it.
The first thought was to get a Webasto coolant heater ( Webasto cab heater is already installed on the truck) for like $1400 with installation, but then I remembered about my 24v 2560 Watt battery.

Bought a 24v inverter for $200 and a $20 timer in Home Depot, ran an extension cord under the cab and plugged everything in.
Timer is set up to turn on 1.5 hours before I get up in the morning (the battery lasting time) and get power to the block heater.

The results are great. The truck starts right away and engine does not sound like it hates me from waking him up. Then I plug in the charger in my regular inverter, start driving and battery is fully charged in about 5 hours.

 

When cord is plugged right in inverter, it shows 1300 watts, however when it goes through the timer, it shows 1000 watts, so battery usually lasts longer than two hours.
I am not sure why it draws less through the timer, because it's rated for 1875 watt and 15a, so there should not be any limitation