I have not been driving my truck as much as I used to, now if I let it sit for a week or so it kills the batteries. I know some of it has to do with the fact that my radar detector is plugged in, as well as the Banks IQ being on stand by.

Well my question is, will my "plug" act as a battery tender as well as a block heater?

No sir....

no, but a good idea.

Get yourself a cheap trickle charger, direct wire it up to one of the batteries, and splice the AC end into the wire for the block heater. Of course that is if you need the heater on when it is just sitting.

I agree on the battery tender. Hard wire it into any circuit that is always on.

I wouldn't "splice" into the 120v block heater wire, unless you know what you are doing working with household voltages (soldering, insulating it, and sealing it from any road salt.)

Why not just have the cords for the block heater and battery tender zip tied together in an easy to reach place and use a 2 or 3 way splitter extension cord?

If you have an updated block heater cord, it will even have a thermostat on it and won't draw power until it cold out (0 or 32f?)

I really dont think I need to use my block heater. My truck sleeps in the Garage. But at the same time, this will be the first winter that it will sit more than it drives.

How do I know if I have the updated block heater?

I would definitely put a trickle charger on your batteries if you aren't going to drive it at least weekly (All of my toys--ATV's and boat batteries have quick connect plugs for a Battery Tender. I charge the boat batteries after I use it, and every month or so in the off season. I keep the ATV's hooked up to them when they aren't being used. I'm just too cheap to buy enough to keep everything hooked up. They are cheaper than a new battery.

To be honest, I would always leave the charger plugged in, but I wouldn't leave my truck's block heater plugged in. There is no point in keeping the coolant warm. It is to make starting easier, not for storage. Just plug it a few hours before you want to use it in the winter and all will be good. The only thing it will do is seriously raise your electric bill.