@cascadian took the words right out of my mouth....it can be very dangerous to use an unmatched pair in a series mod especially drawing the kind of current need to power the loads your putting on them....using only a matched pair of two of the same batteries and rotating their position every other use is the best and safest way to do things....when you stack batteries in series like that one battery is always working harder than the other a little bit as the current from the second battery has to run threw the first and that's why you should rotate their position after every charge to help the wear and tear on them be even.
As was also said above...you're always going to have a voltage drop in any mech mod or regulated mod with a "mech mod" setting.... a voltage drop of .5 is pretty good, especially with mismatched batteries...my best mechs even after their freshly cleaned have a drop of .4 to as low as a full volt depending on the mod, the build I have in my atty, and the age and internal resistance of the battery....and pushing batteries even close while still staying under their max continuous drain limits will still cause their internal resistance to slowly increase over time decreasing their capacity and output with age. The best way to get the longest life and best performance out of your batteries is to recharge them before they drop below 3.5ish volts, rotate their position if using a multiple battery mod, and try not to exceed 80 percent of their recommended max continuous drain limit. Some say storing their batteries standing upright also helps increase their life but I never do so I can't say to that personally if it's true or not. Your best bet is to get some LG HD2's or HB6's or some VTC 3's or 4's running loads like that or at least something like a Samsung 20R/25R or some LG HE2/4's. Others will recommend other batteries but those are the ones I use and can attest to performance and can't say anything about ones I don't have...and you'll want at least 2 if not 3 matched pairs of whatever you buy so you always have a fully charged set and don't have to wait for them to recharge and I recommend the third set so in case you have a long day or something happens and you're not able to charge your drained cells you always have a fully charged set to use and one on standby so you never run out...I've got probably 25 plus batteries I use in rotation for all my mechs and three pairs of batteries just for my Segelei 150 I use and am ordering three more this week when my PVA 40 arrives so I have plenty just for that.
Also, well I am ranting on and on about batteries I might as well rant about chargers for a bit...don't try and save a couple bucks on a cheap ass charger, that can be more harmful to your batteries than anything else by buying a cheap ass charger that doesn't charge them properly and it will cost you more in replacing batteries in the long run....get something quality like an Xtar brand anything or an LUC series at the least. Some people swear by Intellichargers but I think they're junk (that's just been my personal experience with them, other's have had luck with them but I can't recommend them based on my time with the one I had.) best of luck to you, I hope you get some batteries and it sorts things out for you. Happy Vaping most of all
