Razor1973

I have a 2012 BMW 535i M Sport sedan with a manual transmission and over 100K miles in the odometer. This was my primary (only) car until about 4 months ago when I leased a different vehicle (not specifying to avoid going into a discussion about that one LOL). I admit that, since then, I've abandoned the BMW. I haven't driven it once. Two of the tires already had a slow leak before and are now on the ground and my battery is dead. The dead battery is the main point of this post.

I have a NOCO Genius G3500 smart charger/maintainer which I have used to revive a completely dead battery on a Honda Accord before. I attached the clamps to the positive (red) connector in the engine bay and an unpainted piece of metal as I read in a few places online. I left it overnight (about 10 hours) and, in the morning, the only light that was on in the charger was the power light. This is a little discouraging, but I remember this was the case for about 2 nights with the Accord before the charger showed other lights and charged (repaired?) the battery on night 3. I am still hopeful this will happen with my BMW battery. Otherwise, I will need to replace it.

I have three questions at this point:

1. Should I continue to charge this way or should I charge the battery directly from the trunk. I think I read that wasn't the safest option and engine bay is the recommended approach. Does this also apply to a fully dead battery?
2. How do I access the trunk with the battery fully depleted? There is no key hole there. Is going through my back seats the only option?
3. If I have to replace the battery, do I get H9, H8 or H7? After reading a few threads, I believe it should be H8, but I am not sure. Also, must I get a scanner to reset the computer after the battery is replaced (and I guess I would look up the procedure) or do I not have to as long as the specs (?) are the same?

I have never done any mechanical or electrical work on my car myself, but definitely want to try. I am also doing an oil change on my own for the first time. Wish me luck! I just need the car to run first.

Thank you in advance!