If you're dependent on vaping nicotine instead of smoking
tobacco, perhaps you should read this before buying that
next mod or other gear.
500 ml (a bit over a pint) of 100 mg/ml (10%) nicotine base
only costs about as much as a carton of cigarettes. It keeps for
years in the freezer and will make:
1 liter of 20 mg/ml (200 ml of nic base + 800 ml of VG and/or PG)
1 liter of 15 mg/ml (150 ml of nic base + 850 ml
You need at least two "e-cigarettes," a primary and a backup. That includes the battery, where you'll want one to use while the other's charging, as well as the liquid delivery device. Many agree on the need for backups of backups. I also recommend you get at least two USB-powered battery chargers, not only a primary and a backup, but perhaps one for work and one for home. They're inexpensive.
I, and most others, STRONGLY recommend you skip the expensive but weak cigalikes