Charging system or battery, how to tell?

[xsgeoff]

Battery does not seem to want to keep a charge in the bike, but drains really slow.

Full disclosure: The bike sat ~3 years before I got it, I have no idea how old the battery is, so this could just be a bad battery. I've been holding off buying a new one since I plan on stripping the bike this winter and building a seat with a gelpack battery case underneath, among other things.

Problem history: I got the bike running mid-April, charged the battery, it was good for awhile, but quickly lost the "oomph" to turn the motor over (no biggie, I like to kick anyways). Checked the acid specific gravity (all was good) and charged it up before I went on holiday in May/June for 2 weeks, and it was good for awhile with the starter, but eventually lost the power to turn over again. From that charge until about 2 weeks ago (about 2600km), the battery was slowly dying, but no issues. Then I started noticing the bike would occasionally die at idle at stop lights, and was really difficult to start. I figured it was something wrong with the ignition relay not getting enough juice to keep the coils "open". So I charged the battery and the bike ran like new again, started first kick, e-starter worked fine.

Now less than 2 weeks and ~130km later, the battery is seemingly starting to die again (bike stalled twice idling at stoplights on my way to work this morning, and the e-starter has no gumption). All seems to be a bit more strange than just a bad battery, since the bike died while it was running at idle.

So, as a guy who views electricity as witchcraft, how do I go about checking my charging system? Or, could these problems really be caused by just a bad battery?

Sorry for the wall of text...

 

[Brian902]

You need to get your hands on a volt meter, set the meter to DC voltage, probably 20 volts setting, put the red lead of the meter on the positive battery terminal, the black lead of the meter on the negative battery terminal and read the voltage.

Should be 12 volts plus. Otherwise charge the battery at 2 amps for at least 8 hours.

Try test again.

If you have 12 volts on the battery with the key off, begin your test.

Turn on the key, check voltage, it may drop slightly, but make sure head light is off.

Now start the bike and warm it up.

Recheck voltage and rev bike up to 3,000 rpm and check voltage again.

At 3,000 rpm it should be 13.5 volts or more, no less.

If it is less first check the length of the two brushes under the left hand alternator cover.

They should be longer than 7 mm, full length is about 14mm.

Good luck.

And yes there are other reasons for charging issues but this will be a good start to finding the cause.

 

[xsgeoff]

Thanks, man. Exactly the sort of advice I was looking for!

 

[jd750ace]

Get your battery fully charged on the bench. Put it in the bike. Connect a volt meter set to DC volts across the terminals. Turn the key on and record the voltage at this point. Engage the starter and record the voltage at that point. Key on should be less than 1 volt of drop. With the starter engaged, voltage should not drop below about 10.5 volts. When the engine is running you should see 14.2-14.5 volts at 2500 rpm. If the battery decays while sitting you have a parasitic draw from somewhere. Connect the meter set to amps inline with the battery negative cable with the bike off. You should see zero amps. If you see amperage, pull fuses one at a time and note which fuse drops the draw. That will be your parasitic draw source.

 

[grizld1]

If the battery sat for 3 years without charging, it's shot. Once you have a new, fully charged battery in the bike, inspect as directed above.

 

[fredintoon]

Hi Geoff,
here's my quick and dirty alternator check.
Start it up and point the headlight at a wall.
Rev up.
If the light patch gets brighter, it's charging.
If it don't, it ain't.

 

[gggGary]

The battery is lasting long enough that it must not be horrible even though it SHOULD be from sitting. Same for the charging system it must be charging a bit or you wouldn't be going weeks between battery problems. You have the tests to do, report back. It is possible your riding style is not allowing enough charging, lots of slow riding, idling and short trips can pull down a battery also. My wife has a Honda Shadow 750 and it had a weak voltage regulator rectifier She just rides it a few miles to work and back and is a "putzer".
we were charging her battery about every 2 weeks till I got her a new aftermarket VR, then problem solved. It was hard to track down because it was charging "almost good enough".

 

[joebgd]

These bikes love a good battery, def my original; battery worked fine for a season or so I thought but once I got a new one she was real happy.

 

[xsgeoff]

Thanks Gary. Most of my riding the last couple of weeks was just to work and back (only about 4km distance, with a bunch of stoplights) so that could follow your theory. It does seem to be draining faster now though than before, which was what was weird to me.

Still waiting on a multimeter before I can do some readings. My friend keeps forgetting to bring his home from work. I should probably just buy one of my own anyways...

 

[gggGary]

What is your idle set at? The factory spec is 1200 RPM. The engine will idle slower but 1200 RPM is about the minimum speed that won't drag down the battery, even when electrics were new 40 years ago!

 

[xsgeoff]

I'm not 100% sure, since my bike didn't come with a tacho... (It is in the list of planned mods soon), but I am fairly certain it is higher than 1200, I think I have it set a bit high.

 

[weekendrider]

What is your idle set at?
The engine will idle slower but . .

+1
I think this also contributes to cylinder miss at idle.

 

[xsgeoff]

OK, so I grabbed some quick meter measurements (it's already getting late here, and I don't think the families with small children in my apartment block appreciate a revving bike this late):

Battery: Standing at about 12.2/3v
Ignition on, no lights: Dropped to about 11.9v
Engine idling, no lights: Fluctuating between just below 12 to 12.5v
Engine idling, lights on: Dropped to a bit above 11.9v again
Revving the engine: Voltage climbed with revs. Highest I saw was 13.5v, but I don't know the engine speed (again, no tach), so difficult to compare to Brian902's guideline of min. 13.5v at 3000rpm. Headlight definitely got a bit brighter with the engine revving.

Fairly conclusively a bad battery then, or should I still check some other things?

 

[TwoManyXS1Bs]

Here's my personal rules on lead-acid batteries (adapted from ancient shop practices).

Once a battery has gone flat, it's dead.

It may seem to take a charge, and show voltage, but don't depend on it.

Batteries can easily fool the thrifty.

Even more so the hard-headed.

Many lead-acid batteries of the time were semi-transparent. Handy not just to view the fluid level, but to see of any plates are cracked and separating. Could also view the bottom to see how much white lead-sulphate was developing, or worse, shorting the bottom of a cell. Any of these conditions warranted replacement.

There is a one-time trick to return a battery back to temporary service, good enuff to make it back home, but that's it. We won't go there.

Many batteries of yore were constructed flat-plate deep-cycle style. These could be deeply discharged, and saved with proper recharging, if done immediately, but not much more than a few times.

Modern batteries with high cranking amps are constructed differently, using 'sponge lead'. The plates have much more surface/fluid contact area, and act like a larger battery. These don't tolerate deep discharge very well. During recharge, the lead replates differently, and you loose the high surface area. Even worse, the replating can cause the plates and cells to swell, bulging-out the sides of the case. A sure sign of a bad battery.

Once a battery has gone flat, lost its fluid, starts bulging, won't hold a charge, doesn't deliver during a 'load test', it should be considered 'dead', no matter how much it (or you) fools you.

Especially during a full moon...

 

[Xmarksthespot]

motorcycle batteries are generally horrible in terms of life span, every once in awhile you get a special one and it lasts for years. Twomany sums up the issues nicely. I would have expected more than 13.5 volts while the bike is running, but that is probably right, as long as there is more going in than out with the lights on, and the battery is good then there should be no problems. I have been fooled before though by batteries that appeared good, seemed to do all the right things but then slowly bled off.

 

[gggGary]

Even in Europe batteries are cheap? Replace it. Bad batteries tend to break other parts of the charging system. And check the brush length too. While you have the brushes out ohm the rotor, 5.6 ohms is ideal but between 5 and 6 is "acceptable" Much below 5 is too low.