1.5 volts
Onions don't have volts.
Volts
Zero volts.
This will still only produce 12 volts. It will produce 1200 watts. watts is the result of Volts times Amps.
13.5-16 volts DC
none!
A lemon typically produces around 0.5 to 0.9 volts of electricity. This is due to the citric acid acting as an electrolyte that allows for a chemical reaction with the metals used in a lemon battery experiment.
plant onion seed and wait a year, onions are the biennial bulbs
I'm not sure I understand your question. An alternator will have to produce 13 volts to charge a battery at 13 volts. Most alternators are able to produce 14+ volts but the range is 13.5 to about 15.5 volts.
lots
It can produce up to 600 volts. It is not really an eel but a part of the group called knifefish. It is considered an apex predator.
A good AA battery has about 1.5 volts across it.