This is what I think the answer is but I would appreciate a reference or two in support, or to the contrary.
Early oil refineries consisted of batteries, or groups, of batch stills. The term inside battery limits became associated with the equipment in that area. Everything else needed to support the operation became known as outside battery limits. It may go back earlier than that. There were rows of steam boilers at drilling sites. Perhaps they were known as batteries.

HAZOP at www.curryhydrocarbons.ca

Language delights. I trust you, owg.
I always know the meaning for In Side Battery Limits and Out Side Battery Limits, but never imagine the full explanation.
Have a safe day
J.Alvarez

Thank-you, owg.

I'm not in the chemical process industry, so these were new terms to me.  

For the purpose of my own understanding, then,  is it safe to conclude that 'battery limits' in the context of cost engineering are the direct and indirect costs related to the process (IE, process structural supports, piping, process controls, DCS, field instruments).

And in other words, you have your 'major equipment' and everything else to hook up the major equipment to make it work (piping, controls, instrumentation, structural, mechanical, electricals) are covered in ISBL/OSBL factors.

l.

In my previous life as a refinery engineer, ISBL was the process units and everything else (primarily the tank farm, lpg spheres and loading docks) was OSBL.  ISBL was thus a physical boundary.

Lickyu - Jay165 suggests you think of the Battery Limit as a physical boundary. That should help. All capital costs which can be allocated to inside that boundary are ISBL. This would include the ISBL portion of engineering, client costs, etc.

HAZOP at www.curryhydrocarbons.ca

At my place we use the term to define a specific process isolation area for a processing unit as well as a process unit's physical boundaries.  The designation is used for several reasons such as, operating technicians specific areas of responsibility with regard to work permitting, plant drawing areas, and most importantly we use the ISBL/OSBL as a specific isolation point.  We try and design the Unit so that all incoming and outgoing process and utility streams pass through one specific area that can be thought of as the ultimate isolation point.  The thought is that in the case of an emergency there is one point to go to so that the entire processing unit can be isolated from the rest of the plant.