Check your bass batteries too, even if they're newish. The only time I've had batteries die on me during a gig was when I had just put in a "fresh" pair which I'd stored loose in my gig bag. They were OK for a few songs then started to distort on the low notes. I figure they had rolled around a bit and discharged against something metallic or against each other, and now I keep my spares wrapped separately in plastic to prevent possible discharge before they're used.
