1983 BMW R65LS battery/charging probs

Hi,
New to the group. I'm looking for a motorcycle again after ten years
non-riding. Someone nearby is selling a fairly nice looking, low mileage
Beemer but when I went to look at it, they had a trickle charger attached
and couldn't get it started. She said she always had to charge it if it sat
more than two or three days but that is typical of this model. That didn't
sound right to me. Also, I noticed they had not disconnected the battery
while the charger was running which is strongly recommended on every charger
I've ever seen.
Do you think the charger might have toasted something in the electrical
system or did these bikes really have the problem stated?
Thanks,
Tom

 

I would say it is exactly the opposite, there is no reason at all to
disconnect the battery from the bike while charging it. A motorcycle
battery presents a rather significant voltage clamp to a charger.
Unless the charger is defective and is putting out way too many amps,
the battery will keep the voltage down to a level that will protect the
rest of the bike's electrics. Basically the battery would have to have
an open circuit internally, or be boiled dry, plus the charger would have
to be defective, for the charger to damage the bike's electrical system.

Anything's possible, but it is more likely if anything was toasted,
it wasn't the battery charger's fault. My guess is that there is a
leaky diode in the rectifier or a defective component in the regulator
that is draining the battery. I can leave my bike sitting for 6 months
without disconnecting or charging the battery and it will start within
a few revolutions of the crankshaft.

I am no expert on BMWs, but AFAIK this model does not have a bad record
with their electrical systems. There are issues with some bikes that do
not charge their batteries if they are ridden at low RPMs around town,
etc. but that is more a rider education problem than anything else.

I would walk away from this deal, there are plenty of other bikes out
there that have been well taken care of and don't have significant
problems.

 

My bet would be either an aging battery. But could also be worn brushes
and/or sloppy connections. I wouldn't worry about not disconnecting the
battery when attaching a trickle charger. If there's add-on stuff
on the bike, I suppose there could also be a drain evend with the
ignition off, depending on how it was wired.

You want to make sure that there's a "GEN" light when you first turn on
the ignition and that it goes out at about 1500 RPM. If there's no
GEN light initially, you may have an open rotor (about $100-150 + labor
for a rebuilt unit). If the GEN light doesn't go out by 1500 RPM,
I'd look for problems such as brushes or regulator.

None of these problems are insurmountable, but could cost anywhere
from $25-250 in parts. If you don't do your own labor, this adds
up quickly too. Start by looking at the GEN light and find out
the age of the battery.

If you like the bike, I'd suggest springing for an hour of shop
time and having a good BMW dealer give it an inspection. Besides
repair expenses, hopefully this would catch anything that might
be grossly unsafe like a suspension or brake problem. Money well
spent. Ask the dealer and seller if you could do this prior to
the sale.

 

Thanks for all the replies. There is an add on grip warmer so maybe that's
the problem. The owner had replaced the battery once but I didn't ask how
long ago. It's a nice bike but not perfect cosmetically with very low miles
but I think I'm going to let it be someone else's problem/project.
Thanks again,
Tom