Battery issue

[Mainerider]

The '81 R65 I just bought doesn't seem to hold a charge. The seller put a new battery in it in January. I have the receipt. I charged it when I first got it and after a week or two it doesn't have enough charge to turn over the motor. I'm not riding it much but it sure doesn't seem right.
So I checked the voltage at 3000 rpms. 14 Volts. Then I disconnected the negative lead to the battery and checked the voltage between the lead and the battery. 11.9V Then I turned on the ignition: 12.1V that's not good, eh? What next?

Steven

[Luca]

It sounds like your charging system is working with 14 volts at 3k.  If your tests are saying that voltage drops across the battery ground strap (negative lead), I'd make sure all connections are clean and tight.

Is it a sealed battery or a conventional, flooded type?  If it's flooded, you want to make sure that the electrolyte levels are good.

How high are you keeping the revs when you ride it?  You're not really charging until you are consistently in the midrange.  You will also drain the battery more than you can charge it if you're doing a lot of short runs and stop and go riding.

The battery shouldn't drain that quickly just sitting there (especially if it is an AGM), though the cold will reduce it's ability to discharge quickly.  You could try disconnecting the battery ground and measuring current between the negative terminal and frame to make sure you don't have a constant drain on the battery even with the ignition off, such as a (very thirsty) clock or a voltmeter that is hooked up directly to the battery.

[Bob_Roller]

The charging system on the airhead bikes doesn't do much charging, until you get in the 4000 rpm area .

If you are riding the bike at slower speeds than 45 mph, you're not charging the battery when you ride .

[mrbuck]

What is the cca and amphr. rating of the new battery?  It might be new but not the one you need.  Check your owners manual.

[tvrla]

We do need more data, as has already been suggested.

I've been told it takes 15 minutes of more than stop-n-go riding to recharge the battery after a start up.

Does the battery fill the battery box?

It looks like your cables (the negative at the very least) has a LOT of resistance. They are only crimped together and can corrode where the cable is crimped to the end fitting. I'm guessing that's the problem. Was the positive lead checked as well?

That could possibly be the whole problem right there!

[georgesgiralt]

Hello !
If the battery charge get lost with the bike sitting in the shed, maybe you've something eating up electricity ignition off....
With the battery well charged, and the bike turned off I would measure the leaking current. This will ascertain that there is no drain killing the battery.
I use my R65 to go to work every day. In town. around 15~20 minutes ride with the headlight on and my battery holds. I've done this for years !

[Mainerider]

So I should have measured current, not voltage, when I had the battery disconnected. I'll check that after work today. I can check the details on the battery, too. And there aren't any straps holding it down. I'll see if I can swing by Street Cycles this afternoon and see if they have them in stock.

[montmil]

Your R65 uses two flat rubber battery hold down straps. Steel pins extend perpendicular to the strap ends. These are captured in matching metal hooks formed on the battery box. Best of luck finding these at a dealership. I finally made up a pair of short bungees to secure my batteries.

[Justin B.]

Don't buy a new battery just yet...  And, if you do wind up needing one there are a couple of joints we get a 5% discount from...

[Barry]

I agree with Georges. To see if your battery is being discharged overnight you need to measure any leakage current with the ignition off. There should essentially be no leakage and if there is a quick test would be to pull the relays to see if one of them is the cause.

 

[Matt Chapter]

If you are riding the bike at slower speeds than 45 mph, you're not charging the battery when you ride .

That's what 2nd gear is for, Bob!

Your R65 uses two flat rubber battery hold down straps. Best of luck finding these at a dealership.

I did manage to order one (no thank you, just a belt is fine, suspenders would be overkill) from a dealer here in town.. the usual BMW price and service.  $$ and a couple weeks later it came in.

[Mainerider]

I've actually had good experiences so far with he local BMW dealership having everything I've asked for so far. Roundel for the tank, oil filter kit, assorted crush washers, rubber bushing for the shift lever. Everything at or below what I've seen them for online.


Steven

[Luca]

If I caused some confusion I apologize.  I sometimes call the negative battery cable a "ground strap."  The rubber hold-down straps are good to have though... a little extra insurance against accidentally shorting the positive terminal/leads

[Mainerider]

I went for a short ride yesterday after work. She started right up. Didn't ride much, mostly slow local roads. I stopped at the gas station to put gas in the Symba my son is learning on and afterwards the R65 wouldn't start. Just not enough juice. I put it on the charger overnight and this morning I disconnected the negative lead and put the meter to it. Only .8 mili amps. That's not enough to worry about is it?
I haven't looked up the battery info yet.

[Barry]

0.8 milliamps or 800 microamps would take thousands of hours to discharge the battery so that's not a concern.

Even though the battery is almost new it sounds like it's the problem.