Relative longevity of iPod shuffle models: G2, G3, G4

I have a couple of Gen 2 shuffles that I have kept and will loan out to people from time to time. I also have a Gen 3 shuffle and a Gen 4. Recently I was hoping to use either the G3 or G4 while I had some dental work done as I could control either of those without disturbing the dentist.

To my surprise the G3 and G4 were (and are still) completely unresponsive. Their lights do not go on, they are not recognized on the computer, and connected to the proper earphones, there is no sound. They seem to be completely dead - and that is after more than one attempt to charge them.

I was further surprised to see the G2 shuffles spring back to life after charging.

I was wondering if anyone else has noticed similar performance. Were the G2 shuffles better made for longer life? Or since they are a simpler design, does that help them last longer?