Diesel Bombers - 24v cummins won't start

Hi all
I recently purchased a 2001 dodge cummins 24v and it's the first diesel I have ever owned. It has 260k miles on it and was a one owner truck. It has been up kept and the guy I bought it from did do a lot of work to it. The injector pump was replaced at some point a long the way. I went to pick it up last night and the temperature dipped below 25 after being 40 all day. It did start but had to be turned over several times. This morning I went outside and it was real cold last night and cold again today and with the sun its about 20 degrees.the batteries have been replaced this summer but it has been sitting for about 6 months. I ran a few heat cycles before turning it over but it wouldn't start, and I'm not really sure how I can hold it without toasting the batteries? I then proceeded to plug in the block heater and left it for about an hour, and it still wouldn't start. It only has a quarter tank of fuel so from what I understand the mixture of coldness and older fuel maybe causing the problem? Looking for some guidance to avoid damage! I also checked all of the fluids and they were in range of what they should be.