Please check Retrotec USB chargers for the marking shown in the below image.
 
There was an issue with some past DM32 chargers that resulted in not being able to charge the gauge from a fully depleted (0%) battery level. 
 
There will be a letter in the lower right-hand corner. If it has a “D” shown please notify support@retrotec.com so we can send a replacement at no cost.

 

Please contact support@retrotec.com if your gauge isn't working for any other reason, as well.