It would be better to buy the battery yourself and then take it to any mechanic for replacement.
For hybrid batteries you can go to Sultan Ka Khoo or IJP road where there are truck workshops, there are some a lot of shops for JDM car parts.
Take a simple Voltmeter/ Ammeter. Test the voltage of each cell which should be 7.6-8 volts.
There are people in Pakistan that are offering replacement of cells that are weak so that you dont have to change the whole battery but thats the wrong approach since these cells are balanced to each other so a full battery pack is the way to go.