sometimes spade connectors on battery work loose.
can get air locks in pump, need to disconnect hoses to pump.
as said check for kinks inside base.
I undid base and removed all plastic black pipes and put on 8mm microbore hose from yellow body to pump and out of base.
I wish you could get a 12 volt battery that uses eyelet connectors so you can screw down connectors; as spade connectors fall off
hope you sort out mate