I tend to err on the side of safety since I had a battery explode in a mechanical
mod a few years ago. I use 20 amp CDR
batteries (Sony VTC4, AW, Samsung 25R, and LG HG2) and rarely build lower than 0.5 ohm.
Everyone is free to set their own parameters, and I can only say what mine are. I try to never exceed 50% of the CDR (continuous discharge rating) of a fully charged battery (4.2v). So with a 20 amp battery, that 50% would be 10 amps continuous -- a 5.2 amp draw from a 0.8 ohm coil).
The reason that I place a 50% limit is because as a battery ages the mAh of the battery degrades, as the mAh decreases, so does the battery's c rating (amp limit). The battery's internal resistance increases, too.
The capacity loss reduces their run time directly. The increased internal resistance increases the voltage sag you see from them, effectively decreasing their run time even further.
So down the road, your 20A battery may only be a 10A battery.
* Coil amp draw from
Ohm's Law calculations for Mechanical Mods:
1.0 ohm = 4.2 amp draw
0.9 ohm = 4.6 amp draw
0.8 ohm = 5.2 amp draw
0.7 ohms = 6 amp draw
0.6 ohms = 7 amp draw
0.5 ohms = 8.4 amp draw
0.4 ohms = 10.5 amp draw
0.3 ohms = 14.0 amp draw
0.2 ohms = 21.0 amp draw
0.1 ohms = 42.0 amp draw
0.15 ohms = 28 amp draw
0.0 ohms = dead short = battery goes into thermal runaway
Theoretically, you can take a 20 amp CDR battery down to 0.21 ohm. But that doesn't take into consideration on the age and usage of the battery, doesn't consider if it is a rewrap with a deceitful amp rating, doesn't consider that the battery could be a counterfeit brand name battery with a deceitful amp rating, etc.
