Battery at 15+ V, engine off, lights off...
 

... That'll be a knacked regulator then?

Re: Battery at 15+ V, engine off, lights off...
 

Engine off, unloaded battery ... climbed to 15.4 v
Idle, no lights ... 18 v
5,000 rpm, no lights ... 18v
Idle, lights on ... 16v
5,000 rpm, lights on 16v

Re: Battery at 15+ V, engine off, lights off...
 

No wonder I have to keep jump starting the bugger!

Re: Battery at 15+ V, engine off, lights off...
 

To be honest, with those readings, I'd suspect your meter.

Batteries generally can't put out more than 12V. It's the chemistry (six 2V cells).

Re: Battery at 15+ V, engine off, lights off...
 

Have a read through this guide mate. It does sound like reg/rec kaputt but as richy t says try another meter to be sure.

Re: Battery at 15+ V, engine off, lights off...
 

Hmm, I will try that tomorrow, it's a bit dark now!

Re: Battery at 15+ V, engine off, lights off...
 

check the meter on a smoke alarm battery or a car, sounds wrong.

Re: Battery at 15+ V, engine off, lights off...
 

Yep, check the meter. I recently changed my reg/rec and my meter showed the battery as still only charging at 12v. Borrowing a superior meter showed it charging at 14.6v!!

Re: Battery at 15+ V, engine off, lights off...
 

Nicked the battery from the smoke alarm, measured it at 8.5v

Re: Battery at 15+ V, engine off, lights off...
 

Pretty much what I'd expect for a good one.