How can I build a solar powered car charger?
If they are just bare cells, you probably don't have much chance in salvaging all of them.  In my experience of building panels (only a few), I usually end up using 10-20% more panels than actually end up in the panel.

As far as actually building the panel, just solder all of the tabs together in some order (whatever size/shape you are going for), and then mount them between sheets of acrylic. Use some spacers so that the acrylic sheets don't put pressure on the cells.  You can also use some sort of silicone adhesive to hold the cells down to one of the sheets.

As far as charging a battery, you probably want a boost converter to get the panel voltage to a battery charging voltage.  Past that, it should just be a normal lead-acid charge circuit, there are several of these floating around the internet as schematics or off-the-shelf solutions.

Depending on your cells, you may not have enough power to really charge a big battery in any sort of reasonable timeframe, so that's something you may want to consider.