AJ, don't write off the battery tender yet. You can always replace the wires. Three year old batteries can still fail so it is worth keeping your eye on them. If you do not have a good multitester now is the time to get one. It is a tool you should not be without.

As long as you will be at PSL for a few days, disconnect the chassis battery terminals and clean things completely. Leave the terminals off for a few days and monitor the voltages of each battery. If any of them show a voltage drop greater than the others that battery is suspect. Fully charged batteries should sit at 12.6 to 12.7 volts. Corrosion is often a current path to ground and will discharge a battery so as Gary says this is an area that requires periodic maintenance. Come to Sevierville. We can give some more help.

Greg's comment is correct, so if you do replace the battery tender wires just make them the correct length to do the job.