If you are using a regulated mod you are probably ok using the built in ohm reader. That said, I use a stand alone one and recommend the USA ohm meters. They are more accurate than most and not much more ($23+ship)
Sorry for assuming you were a complete noob, I was going off the information given
Read up on ohms law and battery safety. Stream-engine.org is a great tool, but never a replacement for an ohm reader of some kind.
If you are using replaceable batteries, be sure and buy high quality authentics from a reputable seller. I order form rtdvapor and have heard good things about illumination supply, I'd never use Amazon or eBay as there are a lot of knockoffs, and they are hard to spot. I also don't trust batteries from b&ms.
With good batteries get a good charger. Nitecore I or D series are good. Xtar and the efest LUC charger are also good.
Don't know the depth of your knowledge or what mod you are using.. So there is some info
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