Multiple Batteries in Parallel

I use four Gp 27 in series for 48 volts yet store them in parallel with a fifth battery for a trolling motor on a battery tender with a timer for 7 months of the year. Their ages are 2008, 2009, 2012, 2015, 2016. They are diverse and accepting of all and care deeply for each other.

I expect the 2008 to be finished next spring so I'll be introducing a gp 24 to the group.