Has anyone had a look inside an old Garmin GPSMAP plotter. I'm installing an old 238 sounder on a 24' Trimaran, and while it's old, it is perfect for my needs. Like new condition, easy to read in daylight, Big screen, low power draw and it will show me data. Not too worried about out-of date maps as I know where I'm going.

Unfortunately, when turned on, it seems to have no idea what the date is, so takes a while to get a fix. Firmware is from 2005. I suspect a failed internal lithium battery, but before I crack it open I thought this might be a good place to see if anyone's been inside one of these and has any tips.

Lots of info online regarding the smaller 276 series and aviation related units but not these bigger ones.