I need to use Li-ion as a power supply for my PCB. I will use solar power (converted by solar cells with light from the nearest sun) for charging it (or them if I need 2 cells). But the problem is, I've never design or use a circuit like this before. This is not new, so I think you can help me to do this. After finding out for a while, I find that I can buy a CORTEX device of ARM easily in my village. If you've worked with this device, plz help me. Thanks.