Hi @MIKE6236 , as some of the other guys already mentioned you should be safe if you use a good set of batteries from a reputable vendor. There is no harm in doing your own research or asking others if unsure what batteries is best, but most would recommend a visit Mooch's resources on his blog at ECF : https://www.e-cigarette-forum.com/blog-entry/moochs-recommended-batteries.7593/ With mechanical mods, the coil resistance of the build is the most critical factor as that directly affects the current that will flow through the circuit. Common sense is the only thing that prevents people from blowing themselves up. This relates to using Ohms law, a good multimeter and a decent battery or set of batteries with the knowledge to use a coil resistance that would not push the battery limits beyond their design or specs. Unfortunately, a lot of people replace the 'common sense' part with a 'pair of steel cohones' when they build, especially for cloud chasing. When using a regulated mod, the coil resistance is far less of a factor and probably should be the least of your concern. The power that you dial in to deliver to the coil, coupled with what your battery / batteries can deliver is the most important bits. That said, keep in mind that certain mods only supports coil resistances in a specific range, so if the coil is outside that range, the mod typically will not fire at all, or may not deliver the correct or the 'maximum' power. Without going into any fancy details, one thing to note is this part at the bottom of Mooch's recommended battery list that most people miss, ignore or probably just never read: So for a single battery mod using a Samsung 25R, rated as 20A max CDR, you should be OK at up to 60W. With a fresh battery at 4.2v the current draw would be around 15.71 Amps. When calculated at 3.2V or the safe cutoff for Li-Ion batteries, the current draw will be around 20.63A, slightly above what the 25R is rated as. If you have a dual battery mod, the work is divided amongst the batteries, no matter whether they are in serial or in parallel. So for the same 25Rs, you should be safe up to around 120W. For a set Samsung 30Qs rated at 15A (20A when not exceeding 75 degrees C), that would be 45W in a single battery mod and 90W for a dual battery mod.