Yup got it started yesterday. Rode it all of a quarter mile before an ear fell off and I had to go home. I think the battery is toast, but I will withhold judgment until it is warm toast. Reads OK on a meter, but will not load test. I keep a car battery and small cables for just such and emergency.
Tim

► An easy home test is to 1) check and refill the water level in all cells, then 2) trickle charge the battery at (hopefully) less than 1A for 1/2 day. Then (bike NOT running), leave the headlamp ON low beam for 1 minute. While the headlamp is still burning place a voltmeter across the battery terminals. Your reading needs to be higher than 12.0V, hopefully closer to 12.3V.

Charging places a "surface charge" on the battery. It is a superficial charge and not the REAL battery voltage. The headlamp helps burn off the surface charge to reveal a more realistic battery voltage reading.

► Batteries do go "bad"; no doubt about that. But any battery can exhibit signs of poor health because: 1) it's not chemically capable of accepting a charge (it's become sulfated), 2) the charging system is not delivering a proper charge, 3) the system is using too much power, or 4) the owner is simply not riding long enough. Before you go buy a new battery, I suggest you do some investigating to discover what's going on.

• On these older bikes its just as likely that the alternator brushes are worn out, or that the OEM mechanical voltage regulator has given up. A set of brushes is under $5, and modern, electronic voltage regulators (with zero moving internal parts) start at under $20. (If you go with a sealed AGM battery, then you'll need a special "higher voltage" electronic regulator anyway. Call Motorrad Eliktrik)

• It was VERY common back in the 70's to fit 100W headlamp bulbs. (Remember that these bikes can pre-date 24/7 headlamp laws.) The stock bulb was 65W and these super-high wattage bulbs only complicate matters by consuming too much power. Today we can get MORE lumens (and longer life) from a LED bulb that only consumes 25W. 

• Everyone innately understands that 10 minutes on a battery charger is NOT going to make a meaningful difference. However, a lot of owners falsely assume that short 10-15 minute rides WILL make a difference. The charge rates are similar, so how can that be ? When you are riding, you can only count the time spent ABOVE 2800 RPM as meaningful charge time, and you must subtract the time spent at traffic stops because your headlamp is ON and is consuming far more power than the alternator outputs at idle. And to that... discount EVEN MORE if your brake lamp is ON, and then subtract EVEN MORE if your turn signals are being used. This is pure common sense. The mental conception is being incorrectly prejudiced by what your car does on a regular basis, and that is NOT true for your motorcycle.

Hope this helps.

See... https://www.ebay.com/itm/Bosch-Alternator-Brush-Kit-BMW-R-Airhead-12-31-1-244-480-BOALT-Brushesx2/253167027452?hash=item3af1ee44fc:g:-VUAAOSw8-xZw~FM

See... https://www.ebay.com/itm/ALTERNATOR-ADJUSTABLE-EXTERNAL-VOLTAGE-REGULATOR-FOR-BMW-2002-2002TI-2002TII-2L/291676215593?hash=item43e941d929:g:jgcAAOSw--1WsZuM

I also knew Phil and miss him.