I’d highly recommend external charging of the batteries. Unless you are looking at a mod with sealed internal batteries. A lot of mods cannot charge in a balanced manner and will weaken one or both batteries. Check out any decent mod review and the majority of them will tell you to charge externally. Get yourself a good charger as well. I have used Nitecore exclusively and have never had a problem.
I’ve had a few middle-of-the-road mods, Smok, Wismec, Eleaf etc and they all have some issues (minor to major) but will work adequately. If you want to step it up a bit, I highly recommend the Hohmtech Hohm Wrecker G2. Ugly as all get out, but the thing works and works very well. It even does Kanthal TC (I know, but it really does) - or you could go higher and get a DNA mod.
My recommendations
This thing has proven itself as being reliable. It’s powerfull enough for the baby beast, you can choose between 2 or 3 batteries and it’s pretty darn cheap.
A very good charger, you’ll love it. I recommend getting batteries locally from a good battery supplier, maybe state your region and other members can point you in the right direction.
and maybe this for on your keychain
Depending on how many batteries you get you may go a little over the 75, but i think it’s worth it and you will be very pleased with this setup. I would defenitly advice against an internal battery.
Definitely have to agree with @Duchesst about the Opus BT-C series. whether you get the 3100 or the 3400, both are Very reliable and safe units. If you opt for the 3100 though, just make sure you get a v2.2 (or newer, if available).
The benefits of external charging far outweigh having internal batteries, as you’re just putting a self-imposed lifespan on your investment by choosing internal.
As for the best place to buy reputable batteries, IMHO the first stop has to be Illumn.com (the first letter is a capital i) if you’re in the US or don’t mind shipping abroad.
I’ve just had the Opus BT C3100 from gearbeast. It is AWESOME! 
Edit: It’s the v2.2 - just checked!
I can’t believ I have never been to http://www.illumn.com/ I just created an account. They have pretty good prices. They even have flashlights awesome. I have a feeling that they will be my new place for betteries and stuff…
- just goes to show that you can learn something new as long as you want to learn something new.
anywho thanks for giving us your honest opinion.
Hopefully you saw my post earlier in Good Deals?
Turns out, the link Duchesst posted above takes you to the same deal! WOOT! Bonus! =D
Yeah, the last major sale they had, I stocked up on (6) Samsung 25r5’s for $4 each!!! -Definitely a site to watch…not to mention they had LG HG2’s for $5 ea? IIRC.
Man, I really want to get it, I got just enough money, the only problem is that it’s the last of the spending cash. Oh well, I’ll hold off and hope it’s still there next week. thanks again
Quite like the look of this set up, what make and rating of batteries would you recommend
I think lg hg2,samsung q30 or Sony vtc5 depending on the price
At the moment i only use Sony VCT5A in my 3 battery mod and mechs. Must say i’m really pleased with how they work.
Where do you buy your batteries from?.
I buy my batteries from these guys. Trusted company that doesn’t sell clones, all original batteries at good prices.
https://eu.nkon.nl/
Lubrisolve sell hg2’s for I think £8 for a pair. I know quite a few people use their PG and VG.
http://www.lubrisolve.com/index.php?route=product/product&path=20_128&product_id=288
I have that bookmarked. Thanks, E6 to ship to Ireland standard rates. E14 courier.
Did anyone ever buy them from gearbest?.
I looked at gearbest and they are cheapest £11.84 for 4 with free shipping for the Samsung ones
But you have to order just batteries on there own due to shipping regulations
Ok I supose if you don’t mind waiting 3 weeks
I’d be more concerned that they could be clones. Gearbest usually deliver to here in about 8 or 9 days, about the same time as it takes for something to get here from the uk lol