Battery Voltage drops after starting engine
 

I have a question,
When I first start my truck in the morning or after it sits a few mins with it off, I notice my battery voltage drops and jumps a few times till the alternator kicks in then it stablilizes, is this normal for an 07 2500? I had both batterys checked and they are both showing perfect voltage. Its the first Diesel I've owned and I am not sure if its a circuitry issue or normal.
Thanks.

Normal. What's going on is the air intake heater (grid heater) is cycling. It draws some amps, and that's why the volt meter drops.

Thanks,
The previous owner said its always been that way but I wasn't sure.