[Sebastian Alvarez] “So I’m wondering, for event videographers that most likely don’t have a continuous source of power and recording, is it a normal thing to explain these technology shortcomings to the customers and have them sign a waiver?”
No. That would make any sane customer run for the hills. As a professional, it’s up to you to _overcome_ those shortcomings before offering your services.
And, no, you can’t write off lost business due to your waiver.
Here’s what you do – bid on jobs that you can confidently execute with your given level of skill and equipment. In time, that list will grow. Don’t bite off more than you can chew – in business, your reputation is your livelihood.