Hi Mark, I'm not new to vaping and have a little experience, but am new to EFC, maybe I can be of help. The crackling and popping can be normal, it all depends on how high of wattage/voltage you run it at, and many other factors. Sometimes lowering the W/V can reduce the popping, but the vapor will be less potent. The way I always judge if a coil needs to be replaced is if the flavor is becoming muted (loss of flavor) or if it is tasting burnt. Otherwise, I keep using the same coil until one of those two things start to happen with it. If neither of those is happening, and you are not getting enough satisfaction from the vapor, you can either try increasing the W/V for a warmer more intense vapor, or consider moving up to a higher strength liquid. If your using 12mg you can try out 16 or 18mg, ect. If your mod/battery is variable W/V then the battery getting weak will not matter so much as the device can ramp up the power or keep it raised as the battery loses power. If you go to mechanical mods yes you will most likely want to get into rebuildable's, and the battery will become more important too as the power will be whatever the battery provides. Fresh batteries off the charger will be 4.1/4.2 volts. They will lose voltage from use until re-charged, dropping to around 3.5 to 3.2v, you will notice the vapor get less and less over time until you have to put it on the charger again. If you are not ready for rebuildable's quite yet, I can highly recommend an Aspire Atlantis as it provides a very intense vapor without having to rebuild. Make sure you get a proper mod to power it though, like the CF Sub Ohm also made by Aspire, or any Variable Wattage device with at least 20w to maybe 30w.
