For the sake of clarity, the maximum dose of caffeine in an adult is about 400 mg a day, though that will vary by individual depending on how sensitive you are to caffeine, and how fast your body metabolizes it; if you're sensitive to caffeine, you need to aim lower, but it's a bad idea to consume more than 400 mg of caffeine in a day. Also, if you're a teenager/kid, it's recommended you don't consume caffeine at all, but come on, no teenager's gonna listen to that. But I'd recommend hanging around a 200 mg per day dose limit if you're a teen; puberty's takes a lot of energy, your body's under plenty of daily stress, the last thing you need is to flirt with a caffeine overdose.
In mild caffeine overdoses, symptoms include anxiety, fast heart rate, nausea, headaches, and dysphoria. ...Not the gender kind, I mean like just generally feeling Bad. So if you've had a lot of caffeine that day, and these issues happen, it's time to stop now.
And if you really fuck up and take a massive overdose, then you're at risk of seizures and death; that's a concern at around 1000+ mg. You don't need to take it all at once, just over the course of a single day; let's say you start the morning with four cups of coffee, then drink a few cans of pop during the day, and go to Panera in the afternoon and have two cups of that charged lemonade... and now you've got a lethal amount of caffeine in your system.
I mean sure, the charged lemonade is safe to drink if you're an adult with a solid caffeine tolerance, but only if you have one, and only if that's the only caffeinated beverage you consume that day.
Honestly, I don't know what the fuck Panera is thinking, what's the point of selling such an overly caffeinated lemonade while not advertising the high caffeine content? Makes no goddamn sense.
That being said, plenty of energy drink brands these days are pushing high caffeine content as a selling point, so watch out for those. In general, read the labels before drinking, and mind your daily caffeine intake. Seriously, people can die from this even if they're perfectly healthy. Don't fuck around.
Finally, if this has you worried and you're thinking "Oh fuck, i should stop drinking caffeine", that's fine too; a fair amount of the reason why we're so chill about caffeine is because the withdrawal is a cakewalk compared to other drugs. There's no health risks to a caffeine withdrawal, it just feels shitty. Caffeine withdrawal gives headaches, anxiety, difficulty focusing, fatigue, and depression. It'll kick in between 12-24 hours after you stopped taking caffeine, and will last 2-9 days, though the worst of it will be in those first two days. Just stay hydrated, take ibuprofen for the headaches, and try to get more sleep, and you'll be able to get through your shitty withdrawal week without too much trouble.
But if you don't quit, you're probably still fine. Just... yknow, actually check the caffeine contents of the stuff you're consuming, and make sure you stop for the day the second you go over 400 mg.