V-strom (1000) not holding a charge

So here's the deal- When I ride the bike, after a stop or two, I notice the engine is turning over slower than I'd like...and I know that if it didn't start, I'd only have like 1 more try before it wouldn't turn over anymore. Lately, after 2 or 3 stops, I can't re-start the engine, and must bump start it (not a whole lot of fun on a liter bike).

Background-

The battery is older, but seems just fine when charged with a home charger. In fact, I can put it on 2A for 30 minutes, and it will hold at 12.5v and start the motor after sitting for 1 week or more. So, my inclination is that the battery isn't the culprit here (but maybe I'm wrong).

The charging system- after I bump start it, and get it home and charge it back up with a battery charger....I have tested the charging system's output by checking the voltage, while running, at the battery. What I see is usually this-
Idle- 13.9v
off-idle- 14.2v
2,000-5,000 rpm- 15.1V to 15.2V (though I've seen as high as 15.9).....then settles down to 15.0

So, I'm confused because though I see there is possibly a problem with the regulator/rectifier (shouldn't be above 14.6).....why would this cause a DIScharging battery?? I can see how excess voltage could ruin a battery...but why the discharge, only to accept a charge and act perfectly normal later? Seems to me that a 15V charging system would charge the battery perfectly fine, but eventually destroy it (maybe). Why is it just discharging....and working fine once recharged? I'm tempted to start with the easy/cheap stuff (battery) and move up to R/R....then to the stator if necessary. Anyone have any idea what I may be looking at?

How old is the older battery? Sounds like it holds a nice surface charge, but doesn't have the life left to actually crank the bike well enough. Got any friends with spare batteries that you could try?

Replace the battery. The odds of it being something else on the v-stroms is so low you pretty much have to start there.

I'd lean towards the battery, your other stats suggest the charge should be enough to keep the battery fully charged and capable of cranking the engine so it is probably a weak/collapsed cell in the battery.

buy a new Deka battery asap.

Yea....but who else besides me hates to buy a new ____ (battery), only to find out the old one was fine; and the problem was the ______ (not the battery) Guess that's the way to go. I'll get a new battery and see where we are. Keep ya posted.

Have an retail automotive place load test it on the way to get a new battery...

It is easy to remove the battery from your Vee. Take it out and take it to an Auto Zone or parts retailer that can load test the battery. Won't cost you anything and that is really the only way to test a battery.

Your voltage readings seem high. That could be your meter not calibrated.......or it can mean the battery is a cause. 12.5 volts is suspect, borderline at best. The high voltage readings at higher rpm can come from the R/R trying to force charge into the battery. A sulphated battery doesn't like to take charge and the lower voltage readings from it are telling the R/R that it needs to charge at a high rate to build up the battery. The battery will take a surface charge but its ability to store larger amounts of current are gone. You have already had it fail to start, I'll bet money it doesn't pass the load test.