Hi, it would suggest the battery is end of life, and is no longer holding sufficient charge.
This can often be caused by age, not storing it correctly when not in use, or over charging (cooking the battery).
Instructions for handing the batter can be found in section 8 (page 24) of the manual.
It is most likely you need to buy a new battery, however you may be able to revive the battery by charging it and then using it until its discharged, then repeating the process 4-5 times (this is known as cycling the battery), however based on the fact its not even holding one bar this is very unlikely to improve the battery significantly.
Before buying a replacement battery online I would go into a authorised dealer, they can analyse the battery in detail, and confirm this will fix the problem, and also ensure the correct part is ordered and your using a genuine part. Your nearest dealer can be found by going here and searching by your postcode.