Charging rate etc.
Test one:
Battery voltage with NO current consumers 'on' except clock.
Readings with digital voltmeter 12.5 - 13.5 volts (depends on quality of battery)
Test two:
Place voltmeter positive lead probe on positive (+) battery terminal and place in turn the negative (-) lead probe onto the frame earth point, now try the engine /gearbox case for earth. There should be no discernable volt drop (this test is known as volt drop in the insulated earth return circuit) If you detect a volt drop of more than .25volt then try cleaning the earthing points/contact area, cables can become work hardened and create a high resistance to current flow. Perform earth test on alternator body (+ probe on +bat terminal and - probe onto alternator case there should be no discernable volt drop if there is try the mounting bolts to ensure tightness you may even like to add a seperate earthing wire from the engine/frame to alternator case/mount.
Test three:
Place voltmeter (+) probe onto B+ terminal of alternator (this should be permanently live and should give you the same reading as battery voltage (ignition off)
Test four :
Voltmeter across battery, turn igntion on; volt drop should be some where about 0.7 - 0.8 volt approximately (depends upon powered consumables run from ignition on 'only' sat/nav etc)
Test five:
Remove spark plug caps, place safely to prevent shorting to earth, potential fire all the usual H & S stuff etc. Voltmeter across battery, crank her over and watch the voltmeter reading (only crank for approx. 5-6 seconds. Reading will be voltage drop induced by the starter in this case possible readings should be in the region of 10.5 - 9.75 volts (take the reading away from initial battery with no load reading and that is the induced voltage drop)
Test six:
This would normally be a starter under load test for current (amps) consumption, however you are only concerned with the alternator output. So we will assume now that you have established some tangible readings with the charging system under load.
To my mind (if only you knew what readings you had before this worry) as you state that your original battery 'boiled' then I would go for a faulty voltage regulator. On most Bosch alternators the regulator can be replaced very easily and can be seen as either a small protruding 10 pence piece sized component held in by either two torx headed screws or small bolts. The alternative would be a small oblong black plastic encased regulator again easy to replace.
14.8 volts is indicating that the alternator is working flat out most of the time either because the battery is not sufficiently big enough (capacity wise) or you have a very large current drain somewhere. Of course it could be that the regulator is on the boarder line limits of acceptable mass production tolerances.
The fact that the battery boiled dry doesn't necessararily mean its the alternators fault, that could have been caused by (don't take this the wrong way) an oversight on the maintenance schedule..ignoring the battery..
I suppose it could also be that you have too large a battery and a not powerful enough alternator, this is probable what with no heated grips or abs and a foriegn dealer. I don't know but I hope this little info is helpful to you....oi wake up!
The bike is a 1999 1150GS without ABS or heated grips so its got the 14 amp-hour battery & I believe it has the smaller alternator. I had a problem in the south of France last summer & had to fit a new battery because the original (I assume original) one boiled. At the time I put this down to a duff cell or the long run down the motorway in hot weather but I'm not keen on a repeat saga this year. I'm not so clued up on the electrical side of things so any info / advice on this subject would be much appreciated. 
With reference to the maintenance (fair & valid point) of the "original" battery I did check the fluid level before the trip but nowt else (battery wise), which may have been in hindsight a bit risky as I am not the first owner - guess I would have at least had reference data which as you say would but useful now! 
