When I first got my car it started up in the cold no problem, now it won't start unless I plug it in.

Now, I don't mind plugging my car in (I mean the block heater), but does this mean my battery is starting to go?

 

Of course a fresh battery is best. Have you changed the weight of the oil you're running? Maybe you need to be running thinner oil if conditions are extremely cold.

 

No I haven't actually. I just always run 10W 30 all year... maybe it's time to start running a better oil.
What's the best winter oil out there?

 

I'd have the battery tested and go from there.

 

Lighter oil weight will reduce the "load" on the engine when cold. I would definitely step down to at least 5W-30 but wouldn't expect a dramatic "load" decrease. I agree with the post above to start with your battery.

 

1) is your block heater actually working??
2) go 5W30 100% synthetic with a very good filter and that way you can run a few miles more on the oil too. Winter time oil changes suck if you do your own even in a shop,, messy with snow and salt
3) get a battery blanket
4) ensure your cord is working, I use those little light things you can buy at walmart for like < $5 that plug in your cord to show power on.