Offensive/Defensive Relics

Each relic provides 3 benefits to you. Some of these benefits are useful on assaults/skirmish (e.g. Starting Energy), some are useful on defense (e.g. Building Damage), and some are useful for both (e.g. Troop Health). Relics can be swapped out at any time, so you will want to maintain a set of offensive relics (which you will use when doing assaults), skirmish relics (which might be the same set) and defensive relics. When you start playing, equip your set of offensive relics. When you are done for a period of time, equip your defensive relics.

This will ensure you get the best bonuses from your relics while attacking, but also get extra defense bonus when defending.