For the OP problem - could it be the fact that his battery was not factory (overall dimensions were larger), thus the piping does not fit exact.
Not 15cm prob around 40cm until the pod is fully submerged.
Printable View
your intake is different to mine, your pipe is larger diameter, take offs in different angle etc
http://[IMG]http://i56.tinypic.com/112cqc1.jpg[/IMG]