Several problems with this circuit for lithium ion
batteries. First, the five volt regulator will waste almost half of the output from a 9-volt battery in the form of heat from the TO220 while it is regulating 9 volts down to five volts. Second, five volts is too much to charge a li-ion cell, since they are prone to explode at voltages greater than 4.2. To avoid this, you could
throw the pcb from a $4 usb charger in there to properly control the charging voltage and gain a pretty and functional LED indicator at the same time. That would also avoid any issue with the li-ion cell receiving too much current when it is depleted and over-heating. The last advantage of gutting a USB charger is that it will also give you the proper connector for coupling the li-ion cell to your mobile charger.
I would suggest substituting
three AA or AAA cells for the 9v battery and forgetting about the 5 volt regulator as well, but they would have to be 1.5 volts (alkalines). If using a cannabilized battery charging circuit board, however, you could then use four cells of rechargeable 1.2 volt NiCads or NiMHs (or for that matter, alkalines).
