bad battery or bad alternator?

[96eb96]

shouldn't i fix the reason im getting .5V drop on the negative side?

i looked at my haynes wiring diagram and i don't even see alternator wiring on there

14 30A* Generator/Voltage Regulator

does the alternator circuit go BATTERY>GROUND>ALTERNATOR>POSITIVE CABLE>BATTERY? as far as checking the wiring on the negative side is there anything else i can check? where does the negative cable connect onto the frame? it just disappears into a wiring harness underneath the battery tray, i wanted to test cable/frame contact point to negative terminal to see if maybe the cable is causing the voltage drop

.5V is probably acceptable. 12.5V is most likely a bad alternator.