Why do my outlets show 80 volts?
In general true low voltage readings indicate a loose connection in the circuit somewhere. Identify the circuit by turning the breaker off and now find all of the devices and lights that are off or reading 0 volts. Then turn the circuit breaker back on and trace the circuit. If you can find where the devices and fixtures are reading 120V nominal and the next device or fixture is reading 80V. There is a good chance you have found the area of the problem.
Check all splices and connections to see if there is a loose wire. Look for decolorization of the conductor or burnt insulation since loose fittings create heat. I think it would be good advice to check the entire circuit to make sure the problem does not reoccur. If you find more questionable connections. You should schedule to go through all of the circuits and check for the same problem.
Hint: If you check the the conductors at the problem with the voltmeter. Check voltage across each conductors. If you read 80V between the hot and neutral, and read 120V between the hot and ground. You have a malfunctioning neutral. If you read 80V between hot and both the neutral and ground your problem is with the hot conductor.
Safety note: As I stated above loose or malfunctioning connections create heat and do not trip the breaker so there is a chance if a fire hazard. Needless to say it is a dangerous situation and must be found and repaired. If you are having trouble finding the problem. It might be a good idea to call in an experienced service technician and let them deal with it.
Good luck and stay safe.