That explanation was much more informative so I would also guess it is electrical. I don't deal with points very much. Since you just replaced them, as well as the coils, my first instinct would be a bad condensor. I think that after you replace the points/condensors a few times, it would have been more cost effective to install an electronic ignition. Check with
www.z1enterprises.com for a price on a Dyna S and get rid of those points! They ship overseas and have pretty good prices on their stuff. The owner is also a Brit although he is getting as stout as any American! hehe Tell him I sent you. Also, look at the Coil Repowering article on our web site.
Last, given you rode 15 miles or so, you may have a charging problem. It isn't easy to determine just checking battery voltages. An easy and informative test of the regulator/rectifier is to recharge the battery and start the bike. Once running, put a multimeter on the battery in VDC scale and at idle you should see about 12.5 VDC. Rev the engine to 4K rpm and note the voltage. If it goes DOWN, you are likely not getting a good supply of AC from the stator OR you have a wiring issue; normally a loose ground. If the power goes up to about 14 VDC, then it is likely there is no problem with the charging system and if it goes above 14 VDC, then suspect a bad regulator/rectifier.