Battery
 

can you get a lithium battery higher than 16Ah

Yes, but some case styles cannot go that high.

ok many thanks to you

A common universal Chinese rack battery is 20ah @ 48v and 50ah @ 24v, retailing at around £340 here delivered. This naturally will fit almost any bike.

I use 2x 15ah conjoined in-line to give 30ah @ 48v

yeah, but some case styles can not go such high.

for sure, and can fit most bikes

I think Tesla takes those little cells and builds battery packs more than 16ah. ;-)

EM3ev has (or used to) make large packs to go in the triangle of a bike frame. For instance, 52V 22Ah 25R Large Triangle Battery With Bag
14S 52V 9P (22Ah) with high current 25R cell. Obviously you could configure those same cells to be over 30Ah if you wanted a 36 volt battery. That thing weighs 17lbs, so there that...