That addiction sucks. Two cups of coffee still makes my skin crawl, but the difference is that one cup doesn't help me anymore and now I also have blood pressure problems.
The LD50 for caffeine is approximately 150mg per kg. Considering a large cup of Panera charged lemonade is 390mg, a 200lb (~ 90kg) person would need to drink 34.5 cups of charged lemonade to be lethal
24oz / day over here seems to be the average I gravitate towards.
Less than that, and I start wanting more to stay active. More than that and I start thinking I should cut down, or do a drying out week.
Drying out weeks are maximum give-no-fucks weeks. I have experienced fuck-debt, in which I have fewer than no-fucks-to-give. Goths, doomers and beatniks should totally take note.
Technically even 15L is ok. 69.9 servings of 8 fluid ounces is either 15.888L (UK) or 16.538L (US). Not that I would recommend that anyway, you would have issues from the amount of liquid alone...