Californian frame builder Calfee started life in 1987 and have carved a niche as a maker of bespoke carbon frames. You might have seen one of their bamboo bikes over the years. Well now the company is offering their own proprietary internal battery for Shimano's Di2 groupset.
Born out of a desire to tuck the battery away inside the frame and keep the clean smooth lines of their frames, Calfee have developed a custom battery system which is housed inside the seatpost. As well as hiding the battery, an unsightly fixture on sleek road bikes, out of view, the cables can now be completely routed inside the frame.
The company first machine an aluminium sleeve and bond that to the inside of a seatpost, in which the custom battery slides into. A circlip anchors the battery securely into place. Calfee produce the aluminium sleeve to fit any size seatpost, and even aero posts aren't out of the question.
Charging the battering is simply a case of using their adapte cable. This plugs into Shimano's Di2 charger and works with the wiring harness, so you can charge via the front or rear mech, the charger pushing power through the wiring to the battery, so you don't have to remove the post to top up the battery.
As well as the obvious packaging improvements, they reckon it's 8% lighter and battery life is improved, up to 2,500 hours (or 10,000 miles).
The battery is available on all Calfee models but is also available separately to retrofit to most frames. We don't have a UK price at the moment, but in the US it will set you back $700 (which includes the required frame modifications, custom battery, battery charger, installation of the wiring harness and basic paint touch-ups).
David worked on the road.cc tech team from 2012-2020. Previously he was editor of Bikemagic.com and before that staff writer at RCUK. He's a seasoned cyclist of all disciplines, from road to mountain biking, touring to cyclo-cross, he only wishes he had time to ride them all. He's mildly competitive, though he'll never admit it, and is a frequent road racer but is too lazy to do really well. He currently resides in the Cotswolds, and you can now find him over on his own YouTube channel David Arthur - Just Ride Bikes.