Can you charge your phone through a power bank while the power bank itself is plugged into the mains socket and being charged up? The short answer is yes, maybe! Actually this is possible on a number of power banks or chargers, but it is not a feature that is available on all power banks. But if your power bank manual specifically mentions that it has pass-through charging capability, then of course you can do this.
Some manufacturers will warn you that the power bank will age faster if you take advantage of the passthrough charging feature. However, although there is some truth behind this, it does make sense to purchase a power bank which offers this capability then not use it! But some manufacturers like Anker, warn that using passthrough charging will unnecessarily heat up the internal battery in the power bank which will ultimately shorten the battery life. What you need to bear in mind here is that these power banks have a limited lifespan at any rate, in fact most of these devices which use lithium-ion batteries or similar technology start degrading the moment they are manufactured, losing efficiency every day until at some point in a few years time – they will be all but useless. So if you have a power bank which offers passthrough charging, and you need to charge up the powerbank plus your mobile devices, then go ahead and plug everything in at once, a small reduction in battery life is surely worth the convenience of charging all your devices at the same time!
The power banks which offer passthrough charging do tend to be more expensive models, but it is a really handy feature. In addition, some of the latest power banks which use the new USB-C standard, will likely feature a dedicated pass-through USB-C charging port which will be perfect for all the latest and future smartphones, tablets/iPads and Apple Macbooks.