Check this out:
http://www.lenmar.com/universal-clip-charger-w-adjustable-contacts-and-usb-attachment
Reviews say its quite fragile but there is only one other product that is a) universal li-ion charger and b) USB powered. But that other product is only on aliexpress with 5pcs/lot. All others I have seen are AC only.
I needed one for a Panasonic Lumix camera that doesn’t charge via USB, only via wall battery charger - booo
I know its slightly off topic but I am very excited to find it 