If you are new, stick to the CDR of the battery. Use only high quality brand name batteries (Samsung, Sony, LG). If you are worried, simply use a battery with a higher CDR. The run time will be shorter, but you will not need to worry about +/_ 0.01 or 0.02 ohms. Example.. 3000mah at 20A CDR = 0.21 ohm coils at 20A. vs 2000mah 30A CDR = 0.15 ohm at 30A.
CDR is constant discharge rate. This is the amount of amps you can safely pull without damage to the battery or over heating..
Example, if your mod sticks on at 30A draw, using a 30A CDR battery... it will simply continue to fire until drained without over heating. Mind you your atty would likely get pretty screwed, but the battery will not blow up.
Short version.. sacrificing some run time for a cooler battery isn't a bad idea.