I left this originally, given it was already being handled via the support email.
If someone else comes across this, here’s the main information:
In our battery safety information we recommend
5V total voltage (~1.25V/cell) is significantly below the “never” threshold. Attempting to recharge a lithium ion battery with such a low cell voltage may result in fire.
I’m unsure how that 5V reading was determined. If it was the directly measured voltage across the battery terminals (used by our charger, and probably most others) then either the charger is faulty, or the battery is definitely dead and should be recycled. If instead it was the sum of the measured cell voltages (which may be used by our cell checker - I’m unsure how it’s set up internally) then it’s possible there’s just an issue with the cable/connector, which could stop one or more of the cells from being detected.
Voltages can be confirmed with a multimeter, if you have one:
