Hello & Welcome,
Can you tell me how long you have own the unit?
That sounds like it is enough time for the battery to go bad, as these batteries only last about 2.5 years under the BEST conditions.
You can get replacement batteries for these units, and if you are handy with a screwdriver, you can replace them yourself. You can see one such replacement battery at the link below. I am not associated with that site, but I have noticed that they also include any tools that you will need to do the job.
Roadmate 1412 Battery
I hope this helps. Please let me know if you have more questions.
Take Care, Greg A.