1999 DS 48v Problems

[Keepkool]

Hey All;
I have been trouble shooting some issues with my 99 DS and buy process of elimination I believe have found the issue but would like to see what ya think.
This season I have noticed the cart wouldn't last as long is it used to and occasionally it seamed to charge excessively . I stay on top of the battery and always keep the water level correct and the charger is mostly on the cart when not it use.

I did have corrosion on the cables and changed to an upgraded kit of 2agw. after using this weekend I did a load test of all the battery and found this
battery #1 8.7 volt standing but drop to 4.6 volt under load
battery #2 8.6 volt standing but drop to 7.2 volt under load
battery #3 8.6 volt standing but drop to 7.5 volt under load
battery #4 8.6 volt standing but drop to 5.9 volt under load
battery #5 8.5 volt standing but drop to 7.2 volt under load
battery #6 8.6 volt standing but drop to 7.4 volt under load

To me it appears that battery #1 and #4 have a bad cell . do I need to replace all the battery or just the two . I couldn't find a date code but they are around 6 or 7 years old Duracell CG-8 121 min at 75amp.

Is there anything else I should look at before getting new battery ?

Thanks in advance
Kevin

[Swan]

At that age replace them all not worth trying to find 2 old batteries to replace with and no reason to kill two new ones putting them with four old ones .

[Keepkool]

Thank you , That was my thought