Internal battery mod?

I'd probably recommend an Istick. I'm not going to do all your research for you however. I have an older Itaste Innoken mod that is only 30 watts, but has great battery life, so maybe a more modern iteration of that?

Best of luck in your search...

Anna

 

Innokin Coolfire Ultra, Innokin MVP 4.

Many others, but those two are what I would buy.

 

I'd seek out the Tesla Nano 60w. I have 2 of these and don't use them for TC anyway, as it only does Nickel and Titanium. They're small, will accommodate a 25mm tank (which is why I got them) and a charge lasts a long time with it's 3600mAh Dual Cell LiPo Battery. Comes in black, silver, and blue.

Here's a search on some retailers that still have them: VapeCrawler

EDIT: These little beauties can even curtsy, with or without an atty (I've tested it ; not my photo though)... Now, that's one talented mod!

 

Second Anna, suggesting an eleaf I stick, specifically the "iStick Power 80 W", it has an internal Lipo battery of 5000 mah capacity.
It has a "menu" button to enter the TC modes. If you ignore this small button, the complex TC settings stay out if way, you use the iStick Power as a simple non-TC mod. The oversized battery will last you a long time; I use it all day with a Nautilus mini, and charge it overnight.
If you want a native non-TC mod, choice is very limited. I can suggest you the Innokin Cool fire 40 Watt, extremely rugged and reliable. Same price of the iStick Power, but the battery is only 2500 mah.