I've found (possibly due to the climate and geography of where I live, most of my packs fail from black wire. I replace the pigtails on my battery packs and replace switch harnesess every two years.

THe battery packs are usually (I use NiMH) good for about 3 years of abuse. After that I tend to break the pack and use the batteries for "round the house" use.

Never again, shall they find their way into an aircraft lest they cost me it.