Help -- Battery charge status

Basically, I would like to create a battery recharge station that will take a depleted battery compartment and switch it out with a new, fully recharged one. I can figure out piston movements, merge blocks unlock/lock actions. However, I have yet to find a way to basically determine whether or not the entire compartment is charge or even a single battery. How do I do so?

Secondly, I don't have experience with C#, but I would also like to ensure that my pistons have enough time to execute...

Help -- Battery charge status