I was down at a mates house last night and when I was leaving , around about 22.30,the starter motor was slow to turn and the bike was slow to start. We stopped stopped the engine and pushed it into his garage were we put a multimeter on it to see the battery condition,but this time of asking it wouldn't start.

We waited 10 minutes while we tried to fix my dodgy front brake switch ( new one required, see wanted section ) and when we tried to start it again it did so with no problem, the multimeter showed no decrease in volts at idle and a normal charge at 5k rpm.

Could my battery, of unknown age, be dropping a big chunk of charge as I start the bike but as the charging system is working it just recharges and masks the fault ?

Could there be another unknown fault ?

When you tried to start it in the garage, did the engine turn over and what was the battery voltage? If the battery voltage remained > 12 volts and the starter motor simply did not turn over, I would suspect either the starter motor/ connections or the starter solenoid.

The starter turned over but slowly compared to the high speed whine it normally has, we didn't get a reading as it was turning over

When I got back last night I put the bike on charge on a Oxford optimate . Im just after checking it and running at idle it's 14.4v sitting switched off its 12.6/8v and upon starting it drops from 12v to 10v before raising to 14v as the bike begins to idle.

Could it be when I've charged the battery over night it's masking it's fault in holding charge?

From your voltage readings it looks like a dying battery. Plenty of charge when the engine is running but voltage drops under heavy load current when starting. You could also try a load test by simply turning on the headlights without the engine running, battery voltage should remain above 12 volts. If it drops under 12 volts in less than 30 minutes I would be suspect IMO.

Knackered batteries still have what's called a surface charge - they show a healthy voltage until any kind of load is put on them, so voltage on an off-load battery is pretty meaningless. As Magg says, check the voltage with the headlights on. If you want the science there's a nice description here: http://www.smartgauge.co.uk/surf_chg.html

Cheers,
james.

I checked the voltages with the lights on the it dropped from 12.4v to 11.54v then 10 seconds later 11.53v and it kept decrease ( 11.52-11.51v ) every 10 seconds or so , so that's that battery in the bin !

Import thing with batteries is to keep them as close to 100% charged as possible. As soon as they discharge even slightly the plates get a coating of lead sulphate - leave that too long and it crystallises. Too much of that eventually destroys the battery.

Kept fully charged e.g.with a decent maintenance charger (e.g. Optimate) there's no reason a battery won't last for years

Hi, i just had a simliar thing with me fzr4, i thought it was the battery that was on its way out cos it was cranking ok sometimes and really slow others, and was 7 years old so replaced it anyway but i think it was the reg/rec that was going aswell and not charging properly. I measured the volts with new batt and was between 12.4 and 13.7 with lights on or off (running), but wasnt stable, now fitted with a R6 reg and is 14.2 lights off and 13.6 going upto 14v lights on.
I'd deffo get a new battery first, then check voltages again just to make sure mate.
Cheers
Ian