Navman Mio 168 - knackered?

Evening, all - first post, as these gadgets haven't really been on my radar much before.

My mother-in-law has given me a Navman Mio 168 which she used to use purely as a sat nav, but which she says "went funny", after which she replaced it and stuck it away in a drawer.

It has both the mains/USB and in-car chargers, but the former has an 'iffy' looking pin on the side of the connector to the unit. However, both will power it up, but neither give rise to the orange indicator which (according to the manual) indicates it is charging; instead, it goes straight to green and prompts for set-up (although there are brief flashes of orange if the suspect mains/USB connector is wiggled).

After aligning the screen, then entering all the user data and clicking 'OK', nothing has been saved next time the unit is switched on; it simply prompts for screen alignment again.

I'm wondering whether both chargers are faulty (although if they were, I wouldn't expect either of them to power the unit at all), or whether the internal battery no longer holds a charge.

If the latter is true, does anyone know whether the internal battery can be replaced without tools and/or major technical knowledge? Should I just give up and get something else off eBay? Any help or advice would be much appreciated.

[getsurfers]

Sounds like it was charged all the time, and used ltlle which kills batteries.

It'll need a new one.