Zero have used a thin, IP65 rated onboard charger that requires no separate heatsink and fits under the battery box. More details of the generic Calex Mfg charger the Zero charger is based on can be found at
http://www.greenwattpower.com/1300evc.html. I would hope that this is also a low cost charger for Zero (athough the RRP in Australia for a replacement was a very expensive AUD1800 so I'm not so sure).
While we all would like the charger to be faster, there would need to be compromises to the features listed above to achieve higher power output.
The Brammo uses an Eltek Valere 3kW charger @
http://evolveelectrics.com/PDF/Eltek/Eltek%20Guide%20IP67.pdf. On the surface it is a better charger in a number of ways including:
- higher power
- lower weight (although it requires a heatsink to be added)
- smaller volume per kW
- slightly higher efficiency (less heat)
I'm sure others would have theories as to why Zero have not adopted it but given the need for a heatsink and the Eltek's thickness it would not be possible to fit the charger anywhere but under the seat (as I believe Brammo have done) or in the tank area.
I believe that Eltek Valere only sell these chargers as OEM and require a minimum order which might explain why I'm not aware of anyone trying one with a Zero. From my Googling the documentation about the Eltek charger is almost 5 years old which would make you wonder whether they are still being made/updated.
In terms of what other chargers may fit it's really matter of what you can fit in the tank area above the dog box on top of the battery. Brandon has something I believe and Docbass and Burton have chargers that may be shoehorned in there as long as sufficient airflow can be had.
Protomech put out a nice post on this last year at
http://electricmotorcycleforum.com/boards/index.php?topic=3845.msg23644#msg23644