Vectrix VX-1 Battery Pack Problem

Hello all. Lately, I started having a problem with the battery pack on my Vectrix VX-1. I am hoping that someone can give me some advice. My VX-1 is a 2007 model with the original NiCad battery pack. Here is the problem: When I charged up the battery pack, I got a reading of 35 miles for the range and the indicator showed fully charged. After about 3 miles of city driving and a pause for about 4 hours, the reading was down to 24 miles range. I drove another couple miles and then the range dropped to 9 miles, the red battery light came on and the bike went into "limp home" mode. I was able to make it the final mile home at about 10 mph with the range reading 2 miles. The battery charge indicator still read about half full. So, I barely got 6 miles of range out of a fully charged battery pack. Does this indicate that my battery pack is failing and will need to be replaced or is there something else going on that can be corrected? The bike was running fine all summer and this just started happening the last couple times I took it out. I appreciate any advice that can be provided.