Backpack problem

[Spit & polish]

Hi I have a blue backpack as my back up to my Gardiner one and it's rarely used only been used a few times it will pump water if plugged in to the wall charging but the moment it's unplugged it doesn't let out water any ideas?

 

[ched999uk]

Sounds like the battery has died. They really need a top up charge every month or so. If you have a multimeter you could test the battery voltage. You could try and swap batteries between your blue one and the Gardiners one if they fit, charge both and see what happens.