Battery draining

[alehman]

hey everyone,

a question for people more familiar with these bikes than I am. My battery keeps getting drained every two weeks or so even though the charging system is fully functional. It's an AGM-style battery that I just picked up in the fall so in theory it should be able to hold a charge. However, I personally suspect it's how I've been riding the bike that's draining the battery, and that's what I wanted to ask you guys. I live about a half mile from my school and take the bike back and forth a lot without going on longer, more sustained rides. Could that be enough (starting up, quick ride, starting up, quick ride, etc.) to keep the battery from charging?

If not, how can I test the battery to see if it's holding a charge?

[sgtslag]

The best thing to do, is to install a voltmeter, to monitor the health of the charging system.

As to testing the battery's ability to hold a charge, remove it from the bike, charge it fully, with a smart trickle charger (the Battery Tender Jr. is perfect for bikes, and they run around $30 -- install the connector, and plug your bike in every time you dismount...  the battery will always be topped off, and it will last longer, too), then leave it for several days, and measure the voltage without a load:  it should remain at 13.2(?) Volts (AGM's have a higher no-load voltage than do flooded batteries, but I don't remember what exactly).

An AGM should hold a charge, with extremely little internal drainage, for a year, or more.  If your charging system is not functioning, your engine will run solely off of the battery, quickly draining it to nothing.  If you install a Voltmeter/Battery Monitor, you can see if the charging system is working:  above 3,000 RPM, it should read 14+ Volts; if it reads less than 13 Volts, you are running off of the battery only.

One of the best resources for electrical information on M/C's, is this book:  link.  Check your local library for a copy, and spend some time reading it.  It will show you all you need to know to troubleshoot the electrical system, without spending a fortune replacing parts that were in perfect condition...

My favorite battery monitor, is this:  link.  It is expensive (it was less than $50 when I bought mine two years ago), but it is nice.  There are others available for less than $20 (link) -- check Wal-Mart for the units that plug into a cigarette lighter plug (Wal-Mart sells these, as well, for less than $10 -- should have one on the bike if you ever ride out of town, to allow charging your cell phone).  Cheers!

[kandrtech]

The direct answer to your question:  short rides shouldn't prevent your battery from being adequately charged.

An example.  Per the Service Manual, the starter draws 120 amps.  Let's assume that you crank the starter for 5 seconds.  That is 120 x 5 = 600 amp-seconds taken out of the battery.  A "rule of thumb" is that you have to put 10 percent more back into the battery to recharge it.  600 x 1.1 = 660 amp-seconds.

Now, the bike starts - and the battery is being re-charged.  If only 2-1/2 amps is going to the battery, you only need about 4-1/2 minutes running the bike well above idle to recharge the battery.

This simple approach assumes that you're not idling your bike around town (the higher the revs, the greater the output from the alternator) AND that your charging system is working properly - so do that voltage test.  Output should be at 14.5 volts.

[alehman]

Thanks guys. Like I mentioned, the charging system is fine--- about 14.5 volts at 3000 rpm (slightly higher but never higher than 15). The ride back and forth between my school and my apartment is probably only a minute (versus a 10 minute walk), and there are a few stop signs. That might be my issue. I'll try making a point of taking it out for longer when I ride it. I'll also see if the battery holds a charge.

[shinyribs]

Alehman,my bike does the same thing. Like you said,these bikes dont charge at all until 2,500-3,000 rpms. If I putt around in town a whole lot my bike groans when I use the button to start it. These bike have enough torque to cruise 25 and 30 mph zones in 5th gear,but the rpms are way down. If I know I'm gonna be in town alot I just ride in third. Fuel mileage hasnt suffered at all and it sounds betterDefinitely starts better.

IMO,they need to rev to charge. Of course I'm used to SOHC's. Do the DOHC's charge sooner or at idle?

[alehman]

Thanks for the input shiny. As far as I've heard, the DOHC bikes don't break even until 3000 or so RPMs.