I am in agreement there, technically you could start the engine then disconnect the battery and still have a running engine with 12-14 volt reading on the dashboard, as once the alternator has received an excitation current to the rotor (from the battery), it will deliver an output, power the coil, run the engine etc and deflect the gauge
so any info cleaned from the dashboard is inherantly flawed.
Get the battery "drop tested", (no that doesnt mean.
) then if thats ok, reconnect it and with
all switches off (ignition key out) drop a test meter (set to amps)
in series with +ve and look at the current drain, this should be almost nothing, maybe a milliamp for the clock, if it shows anything more then start taking fuses out until it is zero.
Warning dont drop a test meter set to read amps "across" a battery as it will deliver and show short circuit current which is many many hundreds of amps and will fry a test meter before the fuse can blow.
Don't belive me !!!! well in a DC circuit, Current = Voltage/Resitance or I = V/R so I = 12/0.01 (typical short circuit value) = 1200 amps
Warning when using a test meter in series to measure current, make sure it is set to "amps" not Ohms otherwise you will be buying a new meter (see above)
As Duncan rightly says deal with the cause not the symptom