Lights

Maybe you're not sealing the USB charging port properly. If you open the charging port and shove a bit of paper towel in there, does it come out damp ?

If you don't have mudguards, you may be splattering it with too much road slime. Clingfilm is my goto technology for this sort of problem.

Could it be a bit of road gunk that's been transfered to your USB charging lead, and is contaminating each new light ?

Well Exposure lights don't have a standard USB charging cable, they have a different connector. The same chargers (I've tried 3) work fine on my other Exposure light so I'm pretty sure it's the light itself.

I actually went further than cling film and covered the charging port (the only hole/point of ingress) with waterproof putty!