Battery issues

[ltrinidad]

My boyfriend rides a 1980 BMW R65. His byke has been experiencing battery issues forever, meaning it looses voltage and eventually discharges completely, sometimes in just a couple of days. He has taken the byke for repair, but the issues keep coming back. The mechanic already replaced the alternator, the battery itself, DIADOS plate , checked the battery charge system...Any ideas would be greatly appreciated.

Thanks!

[darrylri]

The "DIADOS plate" would be the diode board (rectifier).

The mechanic is just swapping parts and doesn't have a clue.  A charged battery that is discharged in two days is not a small leak.  

I think it's possible on a 1980 model to remove the key from the bike with the lights still on.  Someone will come along and say if that's so.  If it is, you have to be careful not to do this or it will drain the battery quickly.

Otherwise, I would use a volt meter to make sure that the keyswitch is turning everything off, and if it is, there are only a few wires that are actually live at that point so you can check each one to see if there's a bare spot where it's getting a partial short.

You'll need a wiring diagram for the bike.  The Haynes and Clymer manuals have this.

[Bob_Roller]

How is the bike ridden ?

The charging system on these bikes don't do any real charging until the engine rpm's are in the 3500-4000 range .

If the bike is ridden in 'city' traffic, stop and go sitting at stop lights etc. the battery never really gets charged .

How old is the battery ?

Is it a serviceable type, where you need to add distilled water to the cells every few months ?

You can remove the key in the 'PARK' position and the small light bulb below the head light will be on as well as the tail light .

As Darryl has said, going to need to get a maintenance manual and a multimeter,to start checking out the bikes electrical system .

By the way, where on planet earth do you reside ?

There are a lot of BMW groups around the world, most of them will lend assistance to get a bike back on the road again .

[Barry]

I think it's possible on a 1980 model to remove the key from the bike with the lights still on.Someone will come along and say if that's so.

Yes that you can certainly be do that on the early model  - been there done that several times. A good battery can handle this for a few hours but overnight would likely flatten it.

With all the expensive bits already replaced including the battery a good mechanic with a voltmeter should have been able to sort whether the battery is being charged very easily.

1. Before I did anything I would start with a fully charged battery and I mean fully charged. Trying to do any diagnostic work on a partially charged battery can lead you astray.

2. Leave the battery overnight for the surface charge to dissipate and measure the voltage with an accurate meter. A new wet type battery should have a good 12.6 volts and a the other types a little more maybe 12.7 - 12.8 volts.


3. Start the bike and measure the voltage at the battery while gently reving the engine to 3000 RPM. The voltage should rise to at least 13.8 volts but not more than 14.2 volts.

Come back and tell us what voltages are measured on the bike.

[scottyintex]

 My 1980 R65 had such a weak charging system..the battery was always run down. I had to keep it on a trickle charger all the time. I was riding around in a small town and didn’t hit the highway a lot. It just never had time to recharge..short runs, sitting at stop lights suck the battery down. Then I added the side car and the problem doubled. I went over to Gel battery, LED tails light and signal lights....which helped . But finally I followed the advise of some on the forum and went over to a Omega 400. Problems solved!
Your problem sounds a little like mine. But I think you have more than a short run drain. You can leave the lights on and still pull the key out..at least leave the running lights on. But again I doubt that is you problem.

[bjamesw]

I know this is what is fairly described as a 'band-aid" but I liked it anyway.   I put a high amp battery switch under the tank and circumvented the ign switch entirely.   The combination of a weak charging system and liklihood of any number of slow drains here or there even when shut down made me want to isolate the battery entirely. I got a battery disconnect switch at a boat/marine store.   I saw one recently at Harbor Freight for 1/6 the price I paid.  It's directly connected to the battery POS.    I use the kill button on the bar to shut down, but always shut the electrical down with the switch under the tank.  Don't have to worry about losing the key anymore either.