1) A hydrometer tests the DENSITY of the acid/water mix in the battery.A low density reading is bad because there is less "conductor" for the electricity to pass through.
2) A difference doesn't NECESSARILY mean the entire battery is bad.It does however mean that the cell needs the elctrolyte replaced,re-charged,then re-checked.UNLESS THE ELECTRODES IN THAT CELL ARE DAMAGED BEYOND THE POINT OF USE.
3)I'm not familiar with the load tester you are talking about.
4)I would:
Check the electolyte in the battery first and re-fill/re-place as needed (checking the condition of the electrodes at the same time(plates))
Re-charge.
Load test.
Hope this helps,
Charlie
