The K&K Pure Mini is our favorite choice for any nice acoustic guitar. It's totally passive, so no battery is required. But it's also minimally invasive in the guitar, so it doesn't affect your guitar's natural acoustic tone. Nevertheless, when you plug in, the tone it produces actually sounds like your guitar's natural acoustic sound.
More info from K&K Sound:
"The Pure Pickup is our award-winning, signature pickup for acoustic guitars. Installed on the guitar's bridge plate, the Pure Pickup is the the best choice for achieving a rich, natural guitar sound -- even without a preamp!
Our customers tell us that it's the best passive pickup on the market, which means it's the perfect plug-and-play solution for the musician who wants a warm, full-range signal without worrying about cluttering up their instrument, adjusting onboard electronics, or having to remember to change the battery.
The Pure Mini is a 3-head transducer for steel string acoustic guitar. Its position on the bridge plate provides the perfect balance of sound, picking up all the strings without sounding harsh or percussive and "listening" to the sound board to amplify the unique characteristics of your guitar. The result is a warm, full-range signal that represents the true character of your guitar.
TECHNICAL SPECS & INSTALLATION NOTES: Direct installation with superglue gel is required for optimum performance but the system can be carefully removed without damage to your guitar (you may damage the pickup though). This pickup system will fit all standard steel string acoustic guitars."