As You know each battery should be around
8.6v after the charging cycle finishes and they rest for a few hours.
Taking individual battery readings is to make sure a single battery or two are not the cause of the issue.
Measuring the voltage from the charger receptacle is to confirm they are wired properly.
Since the batteries are just one year old and unless you never added any water it would be very difficult to have used all of their chemical elements.
if you have not checked lately, make sure all batteries have water.
The ERIC charger collects a lot of diagnostic information that you can download and review using their free iDAT software.
Get a USB memory stick formatted as FAT32 and follow the instructions in the Delta-Q website to read the diagnostic info:
https://delta-q.com/software-accessories/