i was just thinking about this....

a few points:-

1.) everyone is coming up with new 'standards' for BB diameters with the general consensus being that large diameter is stiffer.

2.) BB axles have also been hollow for a number of years

3.) The BB shell is lowest 'fixed' point on a bike frame

surely, logic suggests that shifting batteries are placed with an enlarged bb shell?... you could also re-engineer some form of switchable kerrs system to recharge the battery on the fly (perhaps a thumb button on one of the shifters to operate when you are lazy pedalling (ie. spinning without really driving the bicycle along, such as downhill). The recharge socket can also simply be through the end of the crank spindle.

have i missed something here?

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Everything you say is possible. But as battery charging is taken care of by plugging the battery into the charger a kerrs system would add weight for little gain. Kerrs has it main uses in electric bicycles but is expensive.

Battery in BB shell well they can be put anywhere. Calfee do them in the seatpost or tube I can't remember. Also battery tech is minituarising all the time making an even larger BB shell unnecessary.

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www.thecycleclinic.co.uk

There are many possible hollow areas like downtube, seat tube and seat post to fit a internal battery. Unless there are obvious benefits, there is no need to introduce a new BB standard