How thick a branch can be safely cut with this saw??

Pretty easily cut through a 10-11" tree, and still had a decent amount of battery left for additional cuts on some 4-5" branches.

Could this saw be used to cut thru a standard railroad tie (7 x 9 )

Yes it would, it wouldn't be fast. This saw is only about 1/6th HP. I used my 8"/18V NiCad saw (B&D) to cut/fit 4" landscape timber retaining wall and the size and weight and ease of use made up for any time lost. Scissors can also be used to mow your lawn.

does it come without a battery and charger

Jim, I haven't even opened the package yet, but I presume it does come with a battery if you buy the $129 version, since there is a version without battery for $74. I don't know about the charger, but on the Black and Decker website one version is offered without a charger or battery. Sorry I can't be of more help

Did you get the oiler problem fixed. Its seems like a lot people having a problem with the manual oiler.

I contacted the manufacturer on this. I was told to prime it 50-75 times for the first use (not in the manual.) It did send the oil to the chain. I'm new to it so I don't know if it will keep it up but I prime it a LOT more than 3 times between cuts. The tool is great so I'm willing to work with this problem so far.