9V Battery Size but Different Voltage?

I was wondering if there are any lithium or other batteries (doesn't have to be rechargeable) that have a standard 9V snap connector. I was thinking of a typical 9V battery but maybe rated at 3.6 or 3.7V instead with higher mAH rating. Does that exist?

An alternative would be to use AAA or AA batteries rated at 3.7V and chain them in parallel, not series. What's a good choice for low-power applications? They don't need to be rechargeable so rechargeable Li-ion batteries seem like a waste (and I think rechargeable ones have higher self-discharge rate than non-rechargeable?) but ultimately I'm looking for capacity here so that's not too much of a concern.

Thanks!

Think I found the answer to my problems with 3.6V dispoable AA batteries with > 2400mAH capacity!

With much digging, a while back I found some 4P-1S AA battery holders. They were NOT easy to find, and the injection molded case had them marked like they were in series (so following the markings would short out the batteries). They didn't have snap connectors on them, but you could add them.

That said, I would hesitate to use the snap connector for non-9v power sources, in the interest of preventing accidental use of a 9v in it's place. I also don't particularly like the idea of using a snap connector with something that can actually deliver high current, since it leaves the conductors exposed where a stray piece of conductive debris could get in and short it out (whether this matters depends how you've packaged your project and who'll be handling it) There are lots of battery connectors available though, so it's just a matter of which one you're most comfortable with.

That point I mentioned above does suggest one reason why batteries in parallel are less common. If you put in a series battery backwards, the output voltage will be 2-batteries-of-voltage lower, and it probably won't draw enough current to do any damage to the batteries (at least immediately). If you put a parallel battery in backwards, you'll short the batteries out, and they'll get hot very fast (this is how you set fire to unprotected LiPo's - AA's will get hot too, but not quite as vigorously - they'll normally melt the battery box (such that they no longer make contact) instead of setting themselves on fire).

Those 3.6v lithium AA-sized cells (LiSOCl2 - lithium thionyl chloride chemistry) sometimes have additional caveats in terms of operating current limits, or poor performance when transitioning from a long period of very low current to a sudden heavy load. Make sure you've read and understood the datasheet - for example, one that I just found reference to online specs max current of 60mA continuous, 120mA pulse - whereas an AA alkaline battery can put out an amp or more - albeit not for very long - and you can buy 3000mAh LiPo batteries a bit larger than AA battery that are spec'ed for 35A pulses (for vaping).

Ahh OK, that makes sense, thanks!