How much can i sell a broken iphone 4s for?

A friend wants to buy my old iphone 4s, its about three years old, the front screen is horribly cracked and the back has a few cracks going through it as well, and on top of that the lock button doesn't work at all. What should i sell it for?

Black spot on iphone 4 home screen?

Ok so the other day I dropped my iphone 4, and there was suddenly a black spot on the corner of my phone, but it only shows on the home screen? I've seen plenty of black spots on people's phones, but they always stay there no matter what app. It's about the size of the square inside the home button. Anyone know what's happening?

I have iPhone 6+ and my battery drains pretty fast after I left it on charger 2 nights in a row?

I have the 6+ and the first few times of completely using it, I mean couple days of charging it and what not, I was getting very long battery usages, but a couple days ago I accidentally left my 6+ on the charger over night and ever since then, my battery is draining fast. Like I charged it last night and kept it on, nothing in background, no Wi-Fi, no cellular or anything on. Location settings for only stuff I would want on and only if it gives me the option to have the location on while I use the app not even when i'm not using the app. When I first got my phone I restored from backup, and I read that it's always good to always setup an iPhone from new/ not restore from backup so I restored it and set it up as new hoping that will save my battery from getting messed up. Did I do something wrong? I feel that keeping your phone plugged in overnight damages the battery. It happened with my 5 and now my 6+. Is there anything that I should or could do?