Ezgo rxv not making 18 holes of golf

[Mpk200]

Hi I have a 5 year old ezgo rxv 48 volt.

I’ve looked after my batteries every month topping levels up and cleaning terminals.
My cart has started to struggle to make 18 holes of golf and then going from 1/2 full on the gauge to straight to orange light and flat.

Recently I’ve had a 48volt to 12 volt converter installled for my lights.All working okay ,but not sure if it’s just a coincidence that I’m now having battery trouble.

The friend that installed the converter had to put the yellow cable (constant 12 volt) to the positive on one of the batteries rather than onto the ingnition switch.

I’ve checked the batteries with a volt meter and get a reading around 12.30 on 3 of the batteries and just under 12.0 on the other.(after 9 holes of golf)

I’m booked in to pick 4 new batteries tomorrow so just hope someone can help,before I spend $1500 on new batteries if I don’t need them.
Thx
Mike