Got myself a Anker Powerbank, to be honest, I don't think the battery life is bad, the system just drains it fast. The power bank last probably just over 12 hours on full charge and is over 20,000 mAh. I doubt is the battery, is just the system, though 3.7V doesn't seem impressive, the same kind in the XL 3ds systems and the 3ds last longer than the switch. Blame the switch not the battery, but they should have made a longer lasting battery to compensate, now is just a excuse to accessorise and pimp out your switch with swag and style.
Basically it depends on what you do with it.
- Turn off auto brightness and turn down the brightness to lowest setting.
- Switch on air plane mode (It disables wifi which does use some battery, but won't allow wireless controllers)
- Pick games carefully. (Battery life depends on games since it effects the system overall performance and usage)
In the end, if you treat it like a cellphone/Tablet (Which it mostly is) then you got the right idea of getting the most of the poor battery.