AVOlio wrotePcandparts will replace the batteries, you need to ask them.
Though since you are passed your warranty period, it might cost you.
Tell them the brand and model number of your ups, also show them your invoice to announce that it's bought from them , they will tell you what kind of batteries you need to replace even if they do not provide the replacement service.
Thank you for the help, sir. I managed to open the UPS and remove the batteries. I checked PCandParts and they do have batteries available that are compatible but I don't know their capacities. My UPS is rated at 1700VA, so I sent them an email to see what I need to do.
Thanks again for your help.