My battery becomes weak

The battery on my Hyundai Elantra was replaced on 8 January 2018 and today is begin to show usually sign..the cranking becomes becomes slow but able to start, the signal light behaving very strange: flickering inconsistent...some time fast and sometime slow.

Lucky I have fitted a battery meter, a good battery will show reading of 12.0 -12.3V but this time it recorded 10.02V..this means the battery is weak.

I know the cause...my Elantra has not been doing good daily running and frequent starting. Daily travel about 22-30km only.. on weekend the car even travel lesser. 

Removed both terminal and hook up to my battery charger. I hope 6 hours of charging is sufficient. If were to perform recondition charge..it will take about almost to 3 days.