there are auto batteries for the 510 and the eGo...
if the saber touch is too big for you there is also the precious that has a touch activated switch and that comes in 3 different sizes...
here are some other problems to look at...
you say that on your friends 510 you've been reusing the cartridges that came with it...over time and refilling the filler in those really kinda get crappy and dont wick so well..and you'll find yourself topping off and getting one or two good drags and then minimal vapor production, because the atty is actually dry...most people replace the polyfil in the cartridges and it makes a difference...should try dripping with that 510 and see if the vapor production is any better..a quick dry burn of the atty beforehand might also be helpful and get the atty back into shape..
also as far as taking a draw....draw slowly into the mouth and then inhale..even if you're dragging slowly directly into the lungs you'll get minimal vapor...just like holding it in longer will produce less vapor on exhale..
I actually bought the 510 for myself and when the manual battery was an issue, i sold it to my friend for half price and then bought myself the pen style ecig. I also ordered some liquid from nuvape and empty carts for both the 510 and my pen style one. The 510 was bought from Dietsmokes and the pen one from a site that was recommended on here that i forget now.
We both tried the carts first that came with the kits. When the vapor levels were wildly inconsistent and mostly weak, we put liquid into empty carts. That seemed to do little except for the first drag or two, then it was back to little vapor coming out. Plus, maybe you could explain this. We both felt that when the vapor amounts were good, the taste was pleasant and smooth. When the vapor amounts were weak which was more the norm, it would burn our throats somewhat. Why is that?
It seems the majority of you folks do the dripping instead of using carts and that probably helps give better vapor and it makes sense as to why since it goes right on the atomizer, but i can't take these units apart with ease like you can. I can use my teeth to pull a dead cart off and push a new one on with my palm, but unscrewing stuff is hard for me.
So i'd have someone fill a few carts for me with the pen style ecig i have and just cap them for when i needed a new one. I also had three batteries/atomizers, so i'd keep them charged and put together. When a battery died, i just grabbed an already put together and charged fresh one and attached a filled cart. Here and there i'd get nice vapor and good taste, but almost without fail, a few drags later the weak vapor and harsh throat stuff would follow even though i'd drag off it the exact same as a few drags earlier where the vapor output was at least somewhat good.
Oh well, hopefully Janty gets in Ego auto batteries soon and i can try it out. I really want to enjoy vaping like so many here do and thus dump real cigs. If this Ego can perform much more consistently, hopefully then i won't get so annoyed and just say screw it, i'll have a real cigarette instead of hassling with this ecig for nothing.