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Does anyone know why my satnav keeps losing the time? I've noticed that when the SatNav decides we're in London (probably 90% of the time) the time displayed on the data screen is incorrect. If I drive for long enough the SatNav will eventually pick up the correct location, and time.
Thinking like a computer geek, is there a battery in the SatNav unit like the motherboard battery in a PC? Or am I barking up the wrong tree?

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A sat nav will usually get its time data from the satellites the same as it gets its location. Some, or at least my Garmin does (and the marine versions do too), have a backup battery so it remembers where it was when last switched off in the assumption it will be in the same place when switched back on to make the startup quicker. So maybe it does, who knows?

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Yes, my handheld GPS units (going back a few years now!) would always be happiest if you switched them on within a few days and a few miles of where you switched them off. If you flew, say, from Germany to Canada and switched on - you could be in for a significant wait.
That satnav in the RR either fires up with the correct location or puts us in Barnett Lane, Barnett which seems to be the default location at least for my car. It takes an hour or so to work out where we really are and then it's perfectly accurate. This makes me suspect that either the almanac data has run out (but noone else seems to have this issue and I'm on the latest disk) or the antenna isn't working very well (but it's accurate once it gets a fix) or the time being off is enough to force the unit to start from scratch with no position carried over from the last time it was switched off.
Or something else!
Weirdness!

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There is probably a battery in the computer much like a lithium cell on a motherboard etc - a CR2025/2032 that is responsible for keeping the last position and time data in volatile memory.

I've never taken one apart so I don't know for sure, but if its otherwise working... then that would be my first guess. Crack it open and see what you can find :)

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From when I pulled one of the P38 nav units apart many years ago (probably 2012 when I got my P38), I don't remember it having a battery in it.

I think from memory, and the image I found of the top side of the PCB that it probably stores it's last location data in EEPROM or flash memory when it powers down. Mine was always thinking it was somewhere else, and would always go back to that location on next power up. I didn't really look too far into it, but I think it is probably the EEPROM or flash memory chip failing and not writing new data to it.

I went with the aftermarket nav route, so didn't dig further into where the EEPROM is on the board, or if it's replaceable, or if it includes anything else in it's memory - firmware or the likes.

I seem to recall a repair service for them somewhere in eastern Europe, but don't know if that is still happening!

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Hmm, I'd have been happier changing a CR2032 than an EEPROM!!
ah well- thanks for the info :)
Maybe it's time to do a conversion to a tablet - and finally get BT music :)