I hope that it is possible to fairly easily replace the battery on these devices. I've had a bad battery in a Sony reader and an ipod and am pretty well sick of it. On the other hand if they can be user replaced then no problem.
I also use a rechargeable toothbrush and have done for about 25 years and the batteries seem to last about 10 years before failing if they are pretty well discharged before full recharge. They are NiMH which is a bit different chemistry to Kobo devices. It seems to me that the batteries last longer if you use the device frequently and recharge it as needed. It seems to be death to the batteries to just leave them for a few months to go flat. They may not come back fully again.
Any one else know anything about this stuff?