Just plug it in whenever you can, even if it's for a few minutes, and you'll be fine. Partial charges cause no harm, according to Battery University. Battery University says that so-called deep discharges – which happen when you use your phone until only a small portion of its battery life is left — wear down batteries. Samsung echoes that advice in a blog post of its own that offers tips on how to extend your phone's battery life. According to Battery University, the lithium-ion batteries inside your smartphones will have the longest lifespan if they're kept between 65% and 75% charged at all times. It's clearly impractical to always keep your phone charge between those levels, but at least you know what's ideal!The second best charge range for batteries inside smartphones is between 45% and 75%. That's probably a lot more realistic for most people on a day-to-day basis. In fact, you could potentially develop a daily routine to plug in your phone at particular times to keep its charge within those levels. But you do have some wiggle room. If you typically keep your phone's charge level between 25% and 75%, you likely won't cause too much long-term damage.Charging your phone's battery from a low 25% charge to 100% will reduce its capacity and shorten its lifespan. In fact, charging from pretty much any amount to 100% is a bad idea. According to Battery University, lithium-ion batteries do not need to be fully charged, nor is it desirable to do so. In fact, it is better not to fully charge, because a high voltage stresses the battery and wears it out in the long run. I've seen a lot of debate about the effects of charging your smartphone overnight. But if charging to 100% causes the most damage to a phone battery's lifespan, you should probably cut it out.