I have three penlights that I use with Eneloops. A Streamlight Stylus Pro, Pelican 1920 and Streamlight Pro Tac. I popped in a 10440 and a dummy AAA and was shocked at how much brighter they all were.
I think the Pro Tac is the best fit for 10440 due to it’s larger head with more mass for heat sinking and ability to use low mode if you need more than a few mins of constant runtime.
I didn’t do any run time tests but based on past experience, 1 x 10440 will have less runtime but be about 50-100% brighter than two Eneloops.
The Stylus Pro is the smallest and lightest of the three. With my dummy AAA and a Li-On it feels like it is empty. My dummy is just an aluminum rod wrapped in electrical tape. it weighs next to nothing but puts out more light than either of the other two with Eneloops. The Stylus Pro was by far the dimmest of the three but it seems they all have approximately the same output with the Li-on cell.
Some circuits seem to work up to 3-3.3v. A liIon battery can be dangerous. Focalprice has LiFe AAAs plus a dummy. Those should give you 3.3V, 3.6V at most. I use LiFe batteries with my AA lights with great success and better safety.
To make a dummy AAA you only need a small diameter rod. I used 1/8” and wrapped with tape. The tape weighs more than the rod. I was thinking of finding some good foam. It really feels like the penlight is empty.
My Streamlight Stylus Pro with 1 x 10440 small and light enough to EDC even in summer or around the house without it sagging your shirt pocket or pants.