Getting a more compact Battery setup for Olight H25 Wave?

Would like to have just one 18650 cell on rear of headlamp & not have to use the large external battery pack at times.
What easy ways are there to achieve something like this?

Could I use the battery pack/holder on my small H15 wave & just wire it up to the H25?

There are other headlamps but none look to have the beam this has or the infrared activation.