Suggestion for readouts:

• Net Power Change (Even if full.)
• Total Power Generation(Not dependent on output, just the energy going in).
• Total Power Usage (Similar to input)
• [Possibly] Time Till Full / Empty

Examples:

Net Power: +3.5 EC / Sec
Power Generation: +5 EC / Sec
Power Usage: -1.5 EC / Sec
Time Till Full: 10 Min 7 Sec

Net Power: -10.5 EC / Sec
Power Generation: +3 EC / Sec
Power Usage: -13.5 EC / Sec
Time Till Empty: 4 Min 23 Sec