Why do you refer to 'will try to bleed the air out of the hydrualic jacks again'. What has this got to do with the sensors?
Please post a model or diagram of the unit.
There are other batteries other than the 9v, why not go 12v then you can get a rechargable lead acid or use 2 x 6v lantern batteries in series.
You can run the sensors direct off the battery and your Arduino through the regulator on the Arduino.
Daz