I'm strictly a 510 user and here's what I do, not saying it's going to work for you but works okay for me:
Filling a cart: I can get about 7 drops in a cartridge but after 4 or 5, I grab a toothpick and stuff it far enough down the side of the cartridge so that I can pull the stuffing out maybe a 1/4" to let the
juice soak down.
After the
juice soaks in, I push the stuffing back in so it's flush with the top of the cartridge and then top off with whatever
juice will fit in there, usually a 1-3 drops more.
I can tell when I'm low on juice due a plasticky burning taste. When I get that taste, then I refill the cart.
When I know my cart is full, and it's low on vapor, then it's battery time.
A fully discharged battery (flashing red) takes between 2-3 hours to recharge on my standard chargers. I have two chargers and rotate the batteries between them.
There is a possibility that you have a bum charger that's telling you a battery is charged when it really isn't also. My very first charger did that, took 10 minutes or less to charge a battery and then the battery didn't last long.
My battery life with a regular 510 manual battery is probably about 40-50 5 second puffs, not outstanding but that's probably a few hours worth of time for me.
I do notice that when I wash my atomizers (rinse under the faucet and blow out only) that when an atomizer is wet with water, it won't produce any or much vapor until the water steams off, maybe 30 seconds of button time total before I get any vapor.
As far as atomizers getting hot, mine rarely get even more than warm to the touch unless I'm boozing and going wild with the thing.
If yours is getting too hot to put your lips on then I'm thinking that's it too dry and you need to make sure that the filling of your cartridge is at least flush with the top of the catridge and nice and wet. I have yet to have a problem with too much juice other than it getting into my mouth but there's still always vapor when that happens.
Good luck..