They are old panels, well before the industry was forced to standardize.
I would go with all 6 in series. For sure.
The V rated of 2.65V, x 5 = 13.25V. Not good. Operation at a very slightly higher voltage than rated greatly reduces the output.
The 13.25V, deduct losses, like wire and a diode, and there is nothing left.
Most 12V PVs are rated at 17~17.5V at max power.
All 6 of these would only be 15.9V. That's a big important 1.1V.
They may be an attempt at "self regulating" panels.
The idea has been abandonded. It doesn't work.
The spec sheet may prove this theory where it deals with regulation, or simply says 'connect a diode'.
ie: 2.65V-0.5V(Schottky diode)= 1 charged cell, with about no chance of overcharging under any conditions.
The saving grace is with 6 PVs in series, the diode loss only happens once.
I don't usually point to a new post, but 5 of these PVs would be operating near (past?) the drop off of the amps output. Same problem this guy has. His problems are from wire losses putting the panels in the situation of operating in the area of voltage where the amps fall fast. Yours would be from just plain starting voltages.
http://www.fieldlines.com/story/2007/4/10/161143/314
A decent solar controller uses mosfets and has much less forward V drop than a diode.
Heavy wire for the run to the batteries will keep voltage losses lower.
Using heavy wire, a decent controller, and all 6 panels will get the most power into the batteries.
Besides, what are you going to do with a single 2V 8A panel?
G-