As indicated by @grahroll above, being an independent store it is highly likely that the battery is a generic/no brand battery of unknown quality.
We have found ourselves that generic/no brand or even dubiously branded (counterfeited) batteries, available online from sites other than the manufacturer, are of poor quality and don’t last long or fail.
It might be worth contacting the manufacturer of your phone to see if they still have OEM replacement batteries for your phone. Hopefully they do, otherwise it will be a bit of potluck to whether any future replacement battery is of reasonable/good quality to provide a good service life.
