Seldom do glider owners care(read) what the regs say about equipment installed. I'm pleased you chased down the documents for your glider battery & looked at FAA guidance. And I'll join the preponderance of folks who get frustrated with regs not being "pertinent" or up-to-date with technology....

But to add a bit to the discussion, IF batteries are on the equipment list when it was weighed, they are not 'optional' payload. They then are considered part of the fixed installation, and glider should have weight placards for minimum solo and max pilot weights based on batteries IN for flight.

No one would argue that the chubby Gil or Concorde battery in the tow plane is 'optional', but it is removable.

For some club ships, with large members who need more payload, the weight & balance and equipment list might be better off with no batteries computed/listed.... and the lighter pilots can treat batteries as removable/installable payload.

I believe the DG restriction lithium of any style was due to an airframe fire.

And I have seen horrific wiring nightmares, and one case of a fuse in the panel allowing a bowed seatpan to short across terminals on the ground. The retired fireman pilot exited like a jackinthebox when I told him the glider was smoking.

Regardless of FAA guidance inflight accessibility of fuses, the origin protection fuse should be very close to a terminal on the battery.

I'll second the recommendation on batteries OUT for trailering. Especially tail fin installs.

Safe soaring,
Cindy B