surely it doesn't matter if your battery goes down to 5%
The cells aren't supposed to have memory according to bosch and the battery will auto shut off before its volts drop too low.
as long as you aren't leaving it that low for long before you top it up to 40-60% I''d imagine any impact on lifetime capacity of the cells would be minimal.
Same as people who never charge to 100%, your probably doing more harm than good, the cells won't all have the same loads and same voltage if its never charged to 100%
at 100% the charger starts balancing the cells and then the bike shuts off when it's finished.
also those powermore bottles are about 400 here in the UK
I've seen 750 watt batteries for 600-700, the price per watt is crazy.
I'd literally buy a second battery over a powermore even if I took it with me and swaped mid ride