English translation: batteries are rated as to how many amps they are able to safely discharge. Amps are just a function of volts (we use 4.2 since that's the maximum your batteries charge to) and resistance (determined by how much wire is in your coil).
You can calculate how many amps you're going to be drawing from the battery (the formula is amps=volts/resistance), but realistically, using good batteries (for example AW IMR 18650's 1600mah) you only need to be sure you don't have a short. If your resistance is any where near the sane end of the scale (.5 to 1.0+ ohms), you're well within safety limits.
You can calculate how many amps you're going to be drawing from the battery (the formula is amps=volts/resistance), but realistically, using good batteries (for example AW IMR 18650's 1600mah) you only need to be sure you don't have a short. If your resistance is any where near the sane end of the scale (.5 to 1.0+ ohms), you're well within safety limits.