The direct question about leakage
The parasitic battery draw should be VERY low - just keep-alive for clock, radio stations and powertrain computer. A few milliamps. You should be able to park a car for 2 months (1500 hours) without flattening the battery. A typical battery is 75 amp-hours. So 50mA would be too much.
If you have draws higher than that, then something is broken, or some aftermarket things was installed and left on. Such as a USB "charger" always plugged into a DC power port, some gizmo plugged into the OBD2 port, a dashcam set to record while parked, or car comfort electronics that have a cellular modem trying to reach an obsolete (e.g. G3) network that no longer exists.
A guess about your alternator
some weird electrical issues where it randomly and suddenly drains the battery, sometimes while driving
Sometimes while driving!!??
No, that's a different problem. That is a faulty alternator. The alternator should be keeping the battery at 100%.
Here's the problem. You have no idea what your battery's state of charge is. You would not notice if the battery was 90%, 20% or 4% full. You notice when it is 0% full and stuff starts breaking! Once I got a low battery voltage light. The alternator had not just failed, it had failed several days prior and the battery finally got low enough to indicate.
So when you say "drains the battery", you really mean "has been draining the battery for quite some time". Or to be more precise, has not been topping up the battery like it's supposed to.
I suspect you do not have a power drain at all. When you come out and find the car at 0% battery, actually the car had been at 2% when you drove in the night before.
So I would focus on the alternator. With the alternator running, the voltage at the DC power port should be over 13.5 volts.