DOEL notebook battery

I am using doel basic model 0703 for about a year. It's been a month since my battery is not giving back up as the battery level suggests. It runs fine when A/C power but when I run it on battery power it merely gives back up for 5 seconds. So where can I get a new battery or replace the battery? P.S: The battery is LI-ION battery pack model-3S1P.