After hydration cell is 100% used (and contain 10k damage inside) it looks like still able to hydrate crops and never removed from inventory.
TileEntityCrop.java:550 {
if (i + itemstack.getItemDamage() > itemstack.getMaxDamage())
{
i = itemstack.getMaxDamage() - itemstack.getItemDamage();
}
itemstack.damageItem(i, entityplayer);
}