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OK, I have a battery that charges OK, holds it's voltage OK but will not start the engine, just gives out the whirring/clicking noise that you always associate with a duff battery.
After jump-starting you can run the voltmeter across the terminals and get 13.5V, so we do have a working/charging alternator.
Went onto YouTube last night, and apparently there are many many methods of battery testing....
1. Load meter
2. voltmeter
3. hygrometer
4. Another meter that measures the cranking amperage - this is the real kiddy, I am led to believe. The one that truly tests your battery's power to do the job.

Now, I have access to the top three, but not the 4th. Has anyone used one of these? Are they worth buying? Etc, etc....

Have you tried "bypassing" the solenoid?

Try shorting an old screw-driver across the two pillars
to see if this makes a difference. This will spark quite
a lot and may make "weld" marks, but you will soon find
out if there is a problem here.

You will need a fairly stout screwdriver as it will have to
be capable of passing starting current amps. An
electricians type would probably melt and weld itself
on permanently, so beware.

Sometimes the contacts inside the solenoids get
oxidised and although you still get a good voltage reading,
they will not pass sufficient current to start the engine.

Ian

Thanks for that. I'll try to give it a go (it's actually on my motorbike and I'm not sure where the solenoid is)!

If it whirrs its working. The Bendix is not engaging in the ring gear.

If you take the battery to any decent tyre place they will test the cranking ampage for you .....

Load meter works fine if you have access to one.
Volt meter works nearly as well. Excessive voltage drop while cranking indicates either low battery sustaiability or too much current draw.
The load meter should tell which.

I would suggest against directly shorting the terminals. Though the theory is sound, sparks near the top of the battery can ignite the free hydrogen gas also found around the battery. This is a by-product of charging.
I had worked at a quick-service and have seen my share of exploded batteries. They tend to cover the worker with acid. In the eyes, mouth, nose etc. Not too fun.

YMJ wrote:Thanks for that. I'll try to give it a go (it's actually on my motorbike and I'm not sure where the solenoid is)!

My, that's tiny writing... Try looking where the main fuse is,
probably quite close to the battery. That's where it has been
on a couple of Hondas that I have looked at.


Starting current will not be so high, so the sparking will
still be less, but the warning about spontaneous combustion
still applies, possibly more so as the tank will be close by.

Could be fuel starvation, from dry... The fuel pump may not
work until the engine is spinning, so you might meed to bypass
the circuitry that makes it work like this in order to prime the
fuel system.

Maybe the sprag clutch is knackered? Or the main fuse
might just need a scrub.

Ian

Depending on the age of it , your bike may not like fully synthetic oil. Most of them use rollers sitting in a track that grip on a journal to turn the crankshaft ( that's your sprag clutch), then when it starts and the crank goes faster than the starter they are no longer engaged. Its a known problem, rollers skidding on the journal.

Of course, this assumes you don't have an electrical issue though!