Or do they have some fundamentally fatal design flaw?

First set worked for a few hours. Second set worked when I tried them in the house but failed to work on the bike.

Yes, they’re charged. Yes, they’re connected. No, I haven’t snapped or mistreated a wire.

Any ideas.

I got some last week and they did about 7 hours worth of commuting just fine. So I’d guess you are very unlucky!

Mine have been fine twice a day on the commute for a couple of months-only had to charge them half a dozen times!!!!

Yes, that was my experience with the first set.

Now, I’ve just fiddled with them and find that twisting the connector where the two wires become one makes them work suggesting a dodgy connection there somewhere. Ho hum.