Newbie with yam ybr125 custom - wont start

[Lexxlizz]

Hi all... Hoping you can help a newbie out.
After having passed my CBT I just bought a little yam 125 58plate only 3days ago, privately.

My other half after test riding for 20min, ran it from the sellers around 6miles home and then rode it for me to an industrial estate this afternoon (nice and quiet) for a quick refresher and confidence building sesh before hitting the road...

Except we didn't get that far.
Of course I stalled it doing a Uturn after about an hour (impressive I got to an hour huh? ) then it just refused to start on the button after that.
We kick started it and it ran fine again until we pulled over at a cash point and again, same thing . Refusing to start on the button and we had to kick start it.

I've now well and truly got face-on with it and it's sat in the rain on my driveway in protest...

A very kind neighbour checked with a reader the battery levels - they were 11v just stood, raising to about 12v on tick over... Giving it some beans made it bounce somewhere between 11 and 12v. He's suggested to me it could be the regulator rectifier, or the alternator (why not simply the battery, idk).

Can anyone offer up any explanation? I've phoned the seller to ask if he'd had any previous problems and surprise he hasn't but was sorry to hear my issue ... But did say in the 2yrs he's owned it he hasn't changed the battery. Could it just be that?

It's going into the local small garage (not stealership) for a full service on Tues next week. So I guess it'll be a question for then. But I'm gutted I can't have a little fun this weekend in the Derbyshire countryside truly downhearted.

ETA: The chap who I brought it from had a 'fail' originally on this years mot (I know so cos I ran a check before buying it) for having the break light out. When questioned he said it'd literally blown on the way to the test centre (stranger things have happened) - just thought I'd mention incase it's relevant.
Seriously, pie & a pint for anyone who's read this far

[Pigeon]

11v is a drained battery.

The fact the r/r can't charge it could mean the r/r is fubar or the stator or ......

Follow the fault finding guide here:

https://www.electrosport.com/technical-resources/diagnosis-center

[ADSrox0r]

If it's not going above 12v while running that means the R/R or alternator is toast. It'll need a new battery regardless because the knackered charging system has dicked it.

You need to get a meter on the alternator outputs, then you'll know which is your culprit.
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Current bikes: '08 VFR 800 VTEC(yo) , '07 ZZR1400 Winter hack: '95 Aprilia 650 Pegaso Currently lusting after: RC30

[Lexxlizz]

Thanks for both replies. I really appreciate it.

After messing about today I've found the earth cable. Cleaned that up.
Found the regulator rectifier (after snapping a clip on the placcy fake chrome guard, I really am a special kind of stupid) and had a gander... Looks alright to me corrosion wise.
And then bought a new battery. Just a cheap acid fifteen quidder for now (Halfords extensive range) and it starts on the button - unsurprising really. It will if it's got any amount of charge in it... Trying now to get my hands on a voltmeter.
Absolutely praying it's not the alternator as that means I've been had. And I have to make the choice to repair or to get rid I'm guessing like on a car, we really don't want the alternator to go? As ££££?

[ADSrox0r]

It's not ludicrous money, fifty quid gets you a new stator. Forty quid is a new R/R.

Then labour charges on top of that if you're not spanner handy.
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Current bikes: '08 VFR 800 VTEC(yo) , '07 ZZR1400 Winter hack: '95 Aprilia 650 Pegaso Currently lusting after: RC30

[Lexxlizz]

Volt meter reading 12v stood, 12.6 on tick over and 13.2+ with revs.
Good to know it won't break the bank to fix if worse case!!

[Pigeon]

Ideally you want >=13.5v and <=14.5v at 5krpm

But 13.2 is there or thereabouts