Hello Kevin,
If it is indeed the original battery, then you can almost guarantee it will be on or near to, it’s last legs.
If you do decide to change it, my advice would be to buy once and wisely - e.g. Varta/ Bosch with their 5 year guarantee grade. On-line suppliers include Tayna and Battety Megastore etc. - there are more, who usually offer beer value for money than who you will buy locally. It’s likely the new battery will have to be coded to the car.
Kind regards,
Gareth.
p.s.
Apologies- overlapped Steve’s reply,