Is it dangerous or damaging to charge your phone overnight?
I’ve been asked this a few times over the years, and I think the answers depend upon your own attitudes to risk and to money.
Is it dangerous?
The risk is that the phone will overheat and cause a fire. It is true that phones will warm up somewhat as they are being charged. In the normal course of things, this is not going to be a problem, but some people do recommend removing the phone from its case (ie the removable case – don’t try to pull the phone apart!). Have you ever picked up your phone when it has been charging and found it too hot to handle? I doubt it. If I’m wrong, though, I suggest you take it into a repair shop and get it checked out. As long as there is a reasonable circulation of air around it, I very much doubt that leaving your phone to charge overnight constitutes a fire risk.
Having said that, if you are the type of person who unplugs your television set at night because you think it’s a fire risk, then I would think you might prefer not to risk charging your phone overnight. If I really had nothing better to do, I could ask Mr Google to find out the relative risks. I suspect that unplugging the TV at night is probably a habit picked up many years ago from the days of valve TVs and that modern TVs do not carry the same risk. I know from experience, though, that I can’t change the mind of someone who does unplug the TV every night so I wouldn’t try to persuade them that charging their phone overnight is not risky. If you feel it’s safer not to charge your phone overnight then don’t do it.
Is it damaging?
You can’t overcharge a mobile phone battery by leaving it connected to the charger. When it’s fully charged it will stop charging. The damage arises not through overcharging but because the life of the battery is maximised if the charge level is kept between about 30% and 80%. So, fully charging it is not optimal from the point of view of the battery’s life expectancy. Moreover, if the battery charge level starts to drop while it is still connected, then it will start charging again. This also (theoretically, at least) shortens the life of the battery.
Phone manufacturers have been trying for some time to get us used to the idea that batteries can’t be expected to last for more than a couple of years (I don’t know why mine last up to four years). Ignoring the hassle of getting it replaced, let’s assume that replacing it costs £36.50. That’s 5p per day over two years. If you can double the battery’s lifetime by not charging it overnight (I doubt that you could), then that is going to save you 2.5p per day – and that’s assuming that you keep the phone for at least four years! Is it really worth worrying about?
Conclusion: unless you are particularly concerned about fire risk, and/or think that possibly saving up to 2.5p per day is worth the hassle of remembering to charge your phone during the day, instead of overnight, then I really wouldn’t worry about it.