That includes N800 batteries. What is not clear to me is what is the limit on the actual number of ‘up to 8gm equivalent’ batteries you can carry.

The phrasing of the rules is ambiguous, the GUIDE TO RULES EFFECTIVE JANUARY 1, 2008 states “Spare Lithium-Ion Battery” i.e. singular

I take 5 spare N800 batteries with me on long journeys. Do I need to aggregate the “equivalent lithium content" of each battery and stop if 8gm is reached? Or am I only permitted to take 1?

The bozo at the check-in certainly won't know and will make an arbitrary decision to confiscate all of your batteries bar one just to be safe and keep their job.

Also don't forget the packing requirements, tape over the terminals and each battery to be in its own plastic bag.