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Is the battery to blame?

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MarkCR750:
My winter hack, a 1991 CBR1000f died on me at the lights recently in neutral, the starter wouldn't spin the engine and the neutral light just dimmed when I pressed the starter button, the bike bumped started easily though so I got the 10 miles home OK, once home it would start on the button , since then I've charged the battery and it's seemed OK for a couple of weeks, a little sluggish on the starter at times, today it cut out at the lights again but started (just) on the button, once home I got the multimeter on it and it showed just over 12v, I started the bike and got 13.5v at 2500 rpm, I switched the lights on and it dropped to under 12v with the engine running!, (I always ride with headlights on btw), the battery was fitted by the previous owner and is relatively new but is a cheap lead acid one, before I splash out £55 on a decent motorbatt battery I thought I'd ask for a second opinion, do you think the battery is the culprit?, cheers Mark.

mike the bike:
Sounds like.  I remember at a tyre dealers that also sold batteries,  They had a piece of test equipment that was, basically, a dead short.  The idea was to short the battery for a few moments then measure the voltage- checking that it recovers. 
It sounds like yours doesn't.

haynes66:
i would say that the problem is stopping at the lights. just keep going!!

3scs:
Don't try this at home I was shown by an old school auto lecy get a set of jump leads connect to battery also connect a multimeter to battery terminals stand AS FAR AWAY from battery as possible wear a pair of goggles short battery for a short while if battery voltage drops below 9.6 it's shot do it outside though not in garage

K2-K6:
The alternator should be able to get above 13.5volts at those revs even with the lights on.

A healthy and charged battery should sit at about 12.6 to 12.9 ish, any alternator output below that range would not really charge the battery.

If you gave the battery a long slow charge for 24hr then record the voltage,  then after a week check voltage again, it should be more or less the same. Anything more than 0.2 0.3 ish drop in volts would indicate that it's not that healthy.

You can do an earth system check, start and run motor and switch lights on,  raise revs to about 2500rpm, measure between bat negative terminal and alternator casing, it should be less than 0.1volts. If it's much greater than that it would indicate that the earth's need attention.

Also that era of bike can have I think voltage reg reporting affected by the kill switch so make sure that's all clean and functioning properly.

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