The correct location to connect +5V and GND, can be found even by
a short look to the C64c PCB. GND occupies large areas on board
generally, especially near the power connector. I chose one of the gnd
legs of this connector to solder the ground level wire. And +5V is the
second after GND which occupies large trace areas. But we need a very
first entry to the +5V trace. So, we again look for a place near the
power connector. Actually there is a good place to solder our +5V wire.
It's one of the legs of R19 resistor, which is connected directly to the
power switch. But, we have to remember that the switch must be off always
for this connection, otherwise a short-circuit happens to the power supply.
Lastly, the +12V wire has to be connected. We need a place after the
regulator circuitry, to connect this wire. And the best place to solder
this wire, as shown in the figure_1, is the positive leg of 1000
microfarad rectifier capacitor C63.
Actually, if you want you can run your C64 with 8 AA type batteries.
Batteries must be grouped by 4, and these two groups must be connected
parallel to a +5 regulator chip. Then the output of the chip must be
connected to the C64c PCB as described above. There is enough room to put
8 AA size 1.2V rechargable batteries in the standard C64c case. To charge
these batteries you need a 9V 100mA source and 10-12 hours. Of course,
you cannot get sound with this battery solution. Instead of the AA size
batteries you can use a car battery with a proper +5V regulator also.