> otoh on the weight of the whole bike it isn't a huge problem.

Why do you say this? Non-ebikes can be sub-16 lbs; ebike battery packs can weigh, like, on the order of 50 lbs. Ebike users sometimes need to lift the bikes (up stairs at home, or on/off transit).

Battery pack weight absolutely dominates the design and utility of ebikes; any double-digit percent factor is very relevant (IMO).

> on the order of 50 lbs

A really large e-bike battery is 4kg. Nobody is riding an e-bike with 50 pounds of batteries. Even the battery pack on a Zero FX, an electric motorcycle, is only 42 pounds.

Huh, you're right. I wonder why the hell people are building 75 lb ebikes if even the large batteries are so light.

That's because the motors are pretty heavy as well, and once you have that much torque available you'll need a frame and rear hub that can handle it too. My biggest e-bike is about 30Kg including a 2.2 KWh battery. Not quite 75 lb but getting there. The basic machine is a Riese&Mueller charger with a Bosch speed pedelec motor and the usual complement of brakes, gearing and bunch of bags. I don't mind the weight, but I've yet to find someone else that likes that bike. It's a bit of a pain to move around with the motor off but once you're on it and riding it's just like any other bike only more powerful and it lasts for a really long time on a single charge.

I don't know either. I think part of it is that some e-bike customers are not otherwise bike buyers and go for the niche of huge-wheeled quasimotorcycle. I recommend keeping e-bike weight under 50 pounds because it is the design limit of the bike carriers on American buses and on Amtrak. There are plenty of e-bikes under 40 pounds even.

I mean: relative to the total weight of an e-bike using one chemistry or another.

A bigger issue is that batteries are often placed in very bad spots (such as riding high on the rear pannier).