I lock my MacBook that I use to work on several side projects on my train commute to my work desk and plug it in to recharge it. I don't open up the lid. Is it ok to use the electricity (it's not the network)?
Buy a second battery and you'll never have to find out.
Doing that. Thanks.
And remember to bring a small screwdriver, since Apple no longer feels that a battery should be changeable without tools.
If you hadn't asked this question I would say yes, but now that you did... no.
there's no earthly way that the employer has any rights over your work in this manner, assuming you can prove it's never opened during business hours. They may, however, have a claim against you for the cost of the electricity. :)
And the product of using that electricity, under a theory of unjust enrichment.
Get an explicit written contract from your employer that your side projects are yours and yours alone (a nihil obstat), and then stop worrying about the small stuff like this.