Any idea which cable he showed you? The main battery cable can get excessive resistance in it but the one that we see showing up more often as a problem is the cable that goes from the battery positive, under the airbox, and into the main fuse box under the hood. The harness itself looks like 4-5 thick red multi-strand wires all crimped together on either end. Typically you can pop the top off of the fuse box and look right at the end of it where it anchors to the fuse box and see if it shows signs of heat or corrosion. If it looks good and you are still in doubt then do a simple volt drop test on it between the battery "+" and where it attaches in the fuse box. Anything much over about .5V will cause you problems. Since we have been seeing problems with these cables any Volvo tech that is in the know is going to be campaigning on these. The last one of these that I did the car was cutting out and had a general lack of power but it would not do it all of the time. This particular car had about a 1 volt drop in that wire and to just look at the wire it looked fine. The other thing is that they tend to be worse when they are good and hot so if you do a volt drop test on it make sure you get it good and hot first and then throw on all of the consumers in the car, i.e. defroster, a/c, high beams etc.

Mark