Advice needed: I'm currently using IPV2s and a CANA and love them, but would like to be able to vape all day and night without needing to charge. Is getting a dual battery mod or better single battery device or better batteries the answer? Are there even such things?
Batteries in parallel will provide you with twice the operating mAh at the same voltage. Batteries in series will offer the same mAh at twice the voltage. So, yes, if configured properly, a parallel box mod will offer longer life than a single battery mod.
However, once you start in with a paired battery setup, those two batteries need to be purchased at the same time, charged at the same time, discharged at the same time. It's best to label them... AND the charger in your device, if you charge in your device, should offer balanced charging (only really important in series devices, but why not ask for it all).
My advice? Get a single battery unit, and carry a couple spares in a case. I hate the thought of needing 4 batteries to keep a device alive around the clock...
OR, get a large capacity LiPo unit like the 4400 mAh iStick 50 or the 5000 mAh eVic VT. Sure, after the 500th charge the battery will have reduced capacity just like the LiPo in a cell phone. However, after 500 charges (a year and a half IF you charge nightly - longer if the mod lasts more than 24 hours per charge), what are the chances that you won't have purchased a different mod?
I have an iStick 50 and I've been vaping on it off and on for 2 days - I alternate with either one of my mechs or one of my smaller mods - and the battery is at about 60%. even my wee lil' iStick 20 lasts 24 hours tootling on a 1.2 ohm coil in an RTA. My DNA 40 only lasts 12 hours of pretty heavy vaping...