alarm issue combined with battery drainage?

Hi.
I have a 525TDS, may/1998.
there are some more recent issues(like 2 months old):
#1
- battery drained one day - was like 3 years old battery, so i thought ok, i´ll buy another one
- I bought a new battery, Varta H3, supposed to be good, after like a week of not driving, completely dead (while parked)
- charged the battery full, took it to local mechanic shop; he says most probably is the alternator; i think also about the FSU(I bought bought both, so i´ll have them replaced in a couple of days when they arrive)

#2
i replaced like 6 months ago the original hood with a carbon one (much thinner,no insulation)
- the "clown nose" blinks rapidly like 10 sec, after resumes blinking at normal pace (i read that this can happen when smth. is not closed, like trunk etc)
- as you see in hood.pin.jpg, that´s the hood alarm switch/sensor (opened the hood,pressed it all the way down, armed the alarm and de-pressed the pin manually - alarm went off, so pretty sure that´s the hood sensor)
- you can barely see in hood.touch.point.jpg where the hood presses on the alarm sensor, so I´m wondering if it presses it all the way down or not (as the hood is much thinner then the original and no insulation); can the "clown nose" issue be related to this? that the sensor is not pressed all the way down, so the alarm considers that something is not locked? any advice on how to troubleshoot this?; also, can this be a reason of the battery drain?

Sorry for the long post and details, just that I thought so much about this lately that i think I need fresh and brighter minds to look into this a bit.

Thanks,
Florin

Disconnect the hood switch to see if the problem goes away. It may also be the cause of battery drain, since the car will not go to sleep if the switch is not open.

hmm, should´t the switch be closed(pressed down position) when the hood is normally closed and alarm on? then the car should go to sleep...or not?

update:
today i put the key in the ignition without starting the car
- went to test#9 on ODB, the battery voltage was around 12.3 V
- started the car, suddenly the voltage dropped to 8.66 until the car actually started (like 2 seconds), then the voltage went up gradually and remained stable in idle to 13.6

is it a normal course of events, or battery drainage during the night/bad battery/alternator problems/FSU maybe?

Thanks for reading this and I hope to get to the bottom of it...