Melex batteries draining w/o use

[netherstar]

My parents have an old Melex but the batteries are draining just sitting in the front yard. Even when they take it straight off the charger the cart will only go for about 10 minutes. And about 24 hours after taking it from the charger, without using it, the batteries will be nearly dead. They have new batteries, always turn off the key, and have disconnected the wire to the dash board components so nothing there is draining the batteries.

If you need a model # to help, you'll need to tell me where to find it. The body was replaced with a custom job long ago so it won't be anywhere on there.