LEDLENSER Powerbank Flex10

I thought about building something like this a few times before I got my iPhone. It steps up the voltage so power can be transferred which takes some power to do that. It has an efficient design so it doesn't use much power for itself when sourcing power. You have to make sure it's turnt off when not being used or it might not turn itself off. I seldom charge my iPhone above 80%. I'm sure it would charge it at least twice from 20% to 80%. I used it to charge both my AirPods and keypad which have small, delicate batteries and felt safe about them even though I manually turn the charge cycle off. It's handy to be able to charge and use both one or two batteries at the same time. It looks well built and with good quality parts so it should last long. I liked it rate off so I bought two more. Now I can get more out of my batteries by inputting and outputting power at the same time and designating batteries in a more predictable usage and efficient use of them. It's not perfect but is very good. The batteries aren't completely independent in the compartments but don't seem to leak power. Sometimes, when placing two batteries in, the second battery can falsely make the level of the first battery go up a notch, (25%), which might mean the energy transfer between them is from an original voltage differential of less than around 0.6V.