Myth: You can always use rechargeable batteries.
Truth: This one is a bit more misleading than false, but it's still important to know that most batteries do have a limited life span of full discharge cycles. Each cycle starts when your device has used 100% of its capacity. This means that if you charge your phone today from 50% to full and do the same tomorrow, that’s a full discharge cycle. Once you go above the amount of full cycles your battery is capable of it will start to lose capacity to store power.
So yes, you can keep on using your battery for a very long time, but once the official "life span" is over, you'll have to be very mindful of how you use it. Hopefully it will only happen once, when you want to upgrade your device.
Bonus fact: Heat will ruin your battery.
As a general rule heat and technology don't go hand-in-hand. Lithium-ion batteries get hotter when they are being charged. Now while it's also a really bad idea to put your phone in the fridge, you should always be mindful of where you place your phone, especially when charging it. Never charge it under direct sunlight or next to other hot electronics a laptop or a working oven. This may not only damage your battery but also the phone itself.