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Indeed. Seems like a very niche market. The only person I know who has actually let a Di2 battery go flat, to the point it stops working completely, is @Cycliste, and all her electronic devices (phone, tablet, laptop) survive on a maximum charge of about 10%, desperately eeking out their last available electrons. For anyone else, who charges their stuff reasonably regularly, it seems rather overkill.
Apparently using this stuff:
http://www.peterwhitecycles.com/ewerk.php