I think the internal battery is defective in my Garmin 2720, is it replaceable. It will not operate on the ac adaptor or without a 12 volt power supply. Does it even have an internal battery?

Steve, September 2007

Yes there is a small rechargeable internal battery (approx 3 volt), if it is not present or flat the Garmin will not boot.Try leaving the unit powered for a few hours and see if the internal battery recharges.
It needs disassembly , some patience , a steady hand and a soldering iron to replace the battery.
You can get a diagnostic screen by holding menu while you turn on the power , use menu to step through.

john B, April 2008

doesn't have an internal battery

Tim, October 2007