I've been playing acoustic gigs with a high-end guitar, fitted with what I assume is a piezo pickup under the saddle (no controls, just a socket where the end pin usually goes). I did one outdoor gig in extreme heat (southern California) and the signal level quickly dropped to almost nothing. First thought: change the battery. No difference. Tried everything back at home, plugged into an Acoustasonic. All working fine. Did more gigs (in cooler circumstances), the system still held up. Until last weekend. Another hot outdoor one, and the level took another dive. Changed the battery anyway, but the one I took out was still strong. There are no other problems, no intermittent noises, no cutting out or crackles. And when it's working, it sounds great. Naturally, I do my best to keep myself and the guitar in the shade during outdoor gigs. Has anyone else ever experienced the same problem? If so, how did you fix it?