3.7V to 12V DC-DC Boost Converter Module, Mini Multi-Function Step Up Board Supports 5V/8V/9V/12V Output with LED Indicator - 8PCS

you can do a small mod to allow USB charging. Charging mod so you can use a 'normal' 30 pin charger. And the board needed for the above 'simple' charging mod. /I get no remunerations for any links presented.