Could have shields recover like how batteries recharge. Have higher shield regeneration when shields are more depleted. Probably would need longer periods of shields not regenerating after taking damage so slow firing weapons aren't discouraged, or have high damaging weapons prevent recharging from recovering as quickly.
@Jip
You can play like me and use zero hotkeys! Limit yourself to 10 apm and relax. It helps that I regularly have players join that run the game at -3. Gives me time to think, make a cup of tea, and clean the house.