I think you will also need to unsolder it from the board. Also soldering the new one in will make it more secure than electrical tape. If its taped in a little janky, and the battery gets dislodged from a terminal, oops no game save.
Buying the theme decks isn't such a bad idea if you need certain cards. I bought the nightfall deck for the 8 or 9 {D} energy and 11 {M} energy and some great supporters, plus some other nice playable cards. People charge a lot online even for basic {D}/{M} energies.
You could definitely...