I assume that you have tested your charging system with a voltmeter, and even better an ammeter, to tell you if you are, or are not, charging.

I also assume that you tested all of your alternators and the wiring.

When the glow plugs 'fire' they do draw a lot of currrent, but that alone cannot damage your alternator, merely make it work hard. Unless it's a dead short, the alternator will produce full output and just stop producing more.

If the alternator does not have enough capacity to power the glow plugs or whatever electrical load is on, the rest of the power comes from the battery.

If the battery, alternator, regulator and wiring are all good, it is possible that you have a current draw while the car is switched off, such as a trunk light that doesn't shut off, or some other 'sneak' circuit that is supposed to be off, and that is draining your battery when the engine is off.

Best Regards,
Jim