Hello and welcome to the forum. Glad to have you here!
An Ohm reader or DMM is a required tool if you are going to be rebuilding.
If you are new to mech mods and rebuildables I highly recommend you spend some time with Baditude (one of our resident battery experts) and visit his blogs. You are now 100% in control of your own safety (and others around you). Make sure you purchase an ohm reader and a voltmeter or DMM so you can measure your builds, check for shorts and measure the remaining charge on your batteries.
Baditudes Blogs. The blogs regarding mods and rebuildables are listed below:
BATTERIES
9. Battery Basics for Mods: IMR or Protected ICR?
* Another essential read to understand which batteries are safe to use in mechanical and regulated mods. Includes a frequently updated list of recommended safe-chemistry, high-drain batteries with their specifications.
11. Deeper Understanding of Mod Batteries Part 1
* For those who want to learn the differences between IMR, IMR/hybrid, and ICR batteries. What do those numbers and letters on batteries mean? What's an amp rating?
12. Deeper Understanding of Mod Batteries Part 2
* Protected vs unprotected batteries - what's the difference? Ohm's Law 101. What is an AW battery? What is an inline fuse? What is stacking batteries?
17. Purple Efest Batteries Not As Advertised
* A cautionary blog that reveals that the purple Efest batteries may not have the specifications advertised. Also includes a commentary on "continuous discharge ratings" vs "pulse discharge ratings" of battery specs.
OHM'S LAW
14. Ohm's Law for Dummies (Vapers)
* My attempt at explaining Ohm's Law in layman terms and how it relates to vaping.
16. Explain it to the Dumb Noob: Ohm's Law Calculations
* As simple as it is to use, some people have a tough time grasping the concept. Warning: Includes graphic photos of mod explosions.
BATTERIES - WHERE TO BUY
Only buy batteries from a reputable supplier (not ebay or Amazon) as there are many counterfeit batteries being sold. Here are several reputable battery suppliers in the US.
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RTD Vapor
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Illumination Supply
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Lighthound
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Orbtronics