Good on you neddy. I have a great hatred for brand-specific oddities, and the exorbitant and extortionate prices for such things. I am sure with diligence you will develop a simple, neat, and cheap alternative. Perhaps a pvc pipe sleeve, a spring and a washer/10c piece? I have fitted my XT17000 with 3x18650's in a pcv strip-frame, with a built-on 18650 charge controller. It all fits in the original position of the 8x1.5v's, and is charged by a 1.5w solar panel mounted on the stem, or any unregulated 12v supply if the need ever arose. Batteries $1.53 each. Panel $5. Controller $5. They can stick their price-inflated gizmos where the sun don't shine.
You could do similar with a 6v (rated- actually near 8v) panel and a 2x18650 charge controller circuit, and a universal 6 or 9 volt dc supply for if you ever ran it flat in the dark.
Or alternatively just keep 2 batteries on charge, in a dedicated (and dirt cheap) 2x18650 charger. Fleabay is your friend.
An 18650 battery bank is also a cheap, light alternative to lead-acid, for high draw applications (e.g. pulse detector). Say, 3 parallel, 3 seriesed (9 batteries) for 12 volt, or 4 parallel, 2 seriesed (8 batteries) for 6/8 volt. A 12v/3w or 6v/6w panel is still small enough to mount on the stem too. The fleabay 18650 controller circuits are rated at 4 amps- ample for any PI battery bank.
I know the nay-sayers will thunder "you will void your warranty". Tough titties. The 78 series regulators used in most modern circuitry are rated from 2.5v above output (e.g 10.5vmin for 8v), to 25v. max. Low dropout regs have even better tolerances.
