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If the gauge is correct then your alternator is overcharging the electrical system. Do the lights seem really bright?
Okay, then it may be that the gauge is just failing. Any shop or even most auto parts stores can quickly check if the system is really at 19 volts. If it is then the alternator may be failed. If it is not then the gauge has failed. If it is charging to 19 volts it can do damage so someone should check that ASAP.
It can burn out most of the electrical parts, including the computer. Yes, it may need a new alternator if it is overcharging but it could also be a wiring or computer issue so a little more in depth diagnosis will need to be done. If it does need an alternator figure between $250-300 installed.