My usually reliable 276C started acting up about a year ago. When plugged into external power (either wall charger, or 12V plug charger), it would show the red "wall plug" symbol for a couple seconds, then would beep, give the "lost external power" warning, then go back to showing the regular blue battery symbol (so running off battery, not external power). After a few seconds, it would then show the red wall plug symbol again, then beep, show "lost external power" warning, then blue battery. This would just continue to cycle this way until I got fed up and shut it down. For some reason, it will not take external charge. If I have a charged battery on it, the unit works fine, but since you cannot charge these batteries without them being attached to the unit, I'm quickly running out of power. It's not the power cords, as I have two of each. It's not the battery, as I have three. It's not the connectors being dirty, as they are clean. Thinking it has to do with the power port itself, but Garmin is no help, as they basically say they no longer support this unit. Anyone have the same problem, and if so, any solution? Thanks.