If your device is charging slower than expected, there's luckily a simple fix for this!
If you are using your console to power your device with a USB cable, it just might not be strong enough to do so.
Though consoles do provide power, some do not provide enough power to charge another device with a USB cable.
Your best bet in making your device charge as quickly as it is supposed to is by using a Wall Adapter that you plug your USB cable into.
On the other hand, if you are already using a wall adapter, it might just be getting old or have a short in it that is causing a lack of power to be transmitted to your device. A new one should fix the issue.