Spain, like essentially all of Europe, uses 230V, 50Hz electricity. On World Standards you can check if you will be needing an adapter.
It’s wise to take a multi-cube so you can share you connection with other pilgrims and don’t need to worry about taking the ‘last’ one for the night.
Alternatively, you can buy a solar-based system. During the day you’ll carry it attached to your pack so it can fully charge. Once you’re at our accommodation, you can plug in your phone and re-charge it for the next day. Remember that it is mostly being connected to Wi-Fi which consumes your battery so make sure you only have Wi-Fi on when you want to use it.
If you have devices with you that work on batteries, here’s a little tip that will lessen the burden you carry: light-weight batteries.
This post is also available in: Dutch