Doublecheck that you have no more acid left in the pack. If the pack is empty, more acid may need to be purchased. You can purchase 1 quart of 1.265 specific gravity acid from a battery store.

If the first 5 cells are full, you can use a turkey baster or other similar tool to even out the cells, making sure that the plates are fully covered.  You may then use distilled water to top off all 6 cells.

Note: Immediately after use, thoroughly wash the turkey baster before use with food.