You would be rather foolish to do this however unless you had intricate knowledge of the particular aircraft wiring system and a voltmeter and ampmeter handy. On the piper archer for example while doing that will liven the main bus and feed into the battery so long as the master switch is on, it bypasses any voltage regulation and over volt cutoff. This if allowed to continue would no doubt cause damage to any electrical devices such as radios etc and could ultimately lead to a wiring loom fire or short.
You would find most aircraft simular no doubt.