Charging issue

I have a 2002 E825 Gem.The batteries in there are about 5 yrs old.The issue I’m having is it will not hold a charge at all.When I charge it and let it sit a few hours it drains down to 50% or lower.If I drive it after a full charge it drains with in 1-2 hrs.I have checked the voltage on the batteries and 5 batteries measure 12.20 or greater and one is at 10.75 to 11 volts.Could the one battery causing this?Any help would be appreciated

For sure but at 5 years you need a new set.

Thank you!!! I will