Welcome Don to HDTimeline, you will find a lot of HD enthusiasts here and plenty of tips in the self help section. Looks like you have a bad battery 12.5 for fully charged battery is a little low and may have a weak or shorted cell. The best way to check is to pull the battery and put it on a battery tender or low current battery charger. While you are at it, clean all the large guage battey cable ends, including the hidden one at the starter, the ground cable bolted to frame and scrape them all with screwdriver or pocket knife till shiny (if you can check the copper strands if visible for corrosion brown or green replace cables). Assemble and coat them all with dielectric grease (HD dealer has it, but automotive parts places can be cheaper).
Once charged, connect everything back up, aim the bike headlight at a mirror or garage door, you will be checking the brightness of the beam when starting your bike...during the cranking (shade tree machanics CCA check), if the lights dim to 1/4 brightness or goes out while cranking, the voltage available for the ignition is insufficient to start your bike and it is likely a bad battery (if run down to 0 charge more than once the battery reserve will be already degraded). Replace the battery, (after charging the new one overnight and repeating the test.
If the headlight dims slightly and the starter cranks and engine starts, run the engine till warm. Get your digital multi-meter (DMM) and put test leads across the battery, initial reading with engine not on is 12.8 or more. Start the bike, it may drop during cranking to 11V at most, but once runing you should read 14V or so, if 13V or less your alternator is weak or the regulator is shunting too much voltage away... Rev the engine a bit and it should never rise above 15V. At this point if you suspect either the alternator or regulator, replace regulator first, it is cheaper and more easily replaced...if the alternator/generator it is more costly and difficult weekend project. JMHO
