usb lipo charger

[kaiDev]

The project
My friend has a system for warming his ski boots, and a solar powered portable usb charger battery pack, and when he is out on a trip (multiple days) he wants to charge the ski boot warmer with the solar battery.

The electronics
The ski boot warmer batteries are
therm-ic ic950
http://www.therm-ic.com/ThermicSoles/Packs/Smartpack-IC-950.html
they are promoted as litium-ion batteries and the charger's output is 8.4v so i reckon they are dual cell batteries.

I do not know the make or model of the solar usb battery but it's usb so it must be 5v and between 500-1000mA.

My plan
I know charging litium batteries can be tricky. So i have found a charging circuit that i want to use
http://www.ti.com/lit/an/slua023/slua023.pdf
to charge a dual cell battery it requiers 9-13Vdc input

My problem
The missing link is a DC to DC converter that can boost 5v to 9-13v. I have searched around and have found the datasheet for LT1302
http://cds.linear.com/docs/en/datasheet/lt1302.pdf
with an application example for 2v to 12v converter. I have duplicated it in LT Spice to test and connected it to a 5v battery and it gives a 12v output. So far so good (i think).
But the application example dose say 120mA so i dont know what happens if the solar usb battery can deliver more than 120mA and i dont know how to test it with output load in LT Spice so i don't know if it wil actualy produce 12v when connected to the charging circuit. I have tested it with various resistor values between OUT and GND but i do not know if that is a good test or not.
Can some one help me in figuring out if the converter will work or if any one has a better idea. i would appreciate sugestions.



LT Spice file:
http://kaidev.net/charger/voltage%20converter.asc (right click > save as)

[peter.mitchell]

Depending on the Solar usb Battery, it may actually be easier to just modify it to provide a higher output voltage to charge the pack.
However, also, depending on the solar usb battery and the power usage of the "therm-ic ic950", this may be completely impractical (if it draws too much power, or if the solar battery pack doesn't store enough charge or if the solar pack does not charge fast enough ect)

[kaiDev]

I agree that it would bee easyer to modify the solar usb battery but that would make it imposible to chare any thing else like a phone or any thing built to charge from usb. I was hoping to make a circuit that connects with a mini or micro usb.