www.boxertrix.com

What with the lockdown and all I haven't ridden my '01 R1100S in several months. Yes, I know, bad for the bike, bad for me. That needed to change.

I attached my cheap float charger overnight just to be sure the battery was charged enough to get it started. It cranked hard and fired right up for the ride the next day. I went for a ~30 minute ride. Very near the end of my ride, about 5 minutes from home, at a red light I stalled it by dropping it into gear before I got the clutch released. My rusty skills showing there! When I hit the starter button it barely cranked and after a couple of tries it cranked no more. Dead Battery! Luckily I was at the top of a hill and was able to bump start it. The ride home took all of 5 minutes. After I parked and got my gear off, I tried starting it again. Cranked hard and started right up. I repeated that 4 more times. It cranked hard and started each time. The next day it cranked hard and started right up. I went for another ~30 minute ride (no stalls!) and parked as usual after the ride. Time for another ride two days later. This time I got about 2 revolutions of the motor before the battery died. Ughh, what's up with this?

I put the float charger on overnight and the battery measured about 17 volt across the terminals after it charged overnight. The bike started right up and after idling for a bit I measured the voltage across the terminals, while the engine was running, at 20 volts. I removed the battery (and discovered the battery was labeled as installed July 2010! Well done Odyssey PC680!!) and took it to a local auto parts store where I had the battery "tested". The tester showed 17 volts and under load it dropped to about 10 1/2 volts (the testing machine had that as the "weak" zone). It was tested several times with the same results. Back to the garage and back on the float charger (where I measured 17 volts across the terminals while on the charger).

My 87 year old father, who a retired physicist and electrical engineer, first was of the opinion the almost 11 year-old battery was bad (bad batteries can charge to a higher voltage at times he said). Then he changed his mind to the voltage regulator being bad. Then he said the float charger might be bad too. Then he shrugged and turned back to his email.

Any ideas on what is wrong or how to further narrow it down?

My 5 pence worth...
You really only know the health of a battery when it's under load. The fact yours measured 'weak' when tested that way would be reason enough to replace it. That and the fact it's over 10 years old is another.

Also 20 volts across the terminals when running, that sounds high and also could be caused by a duff battery, I'd expect 14.4 volts or there abouts.

For the sake of changing to a new battery (£50-60) is it not worth starting (no pun intended) out along that path?

https://www.tayna.co.uk/motorcycle-batteries/f/bmw/r1100s/

I agree with Fuzz, change the battery - it'll be collapsing internally.
You should only get 14.4 to 14.5 volts on charge for a brand new one.
That's where I would go (Tayna) too - excellent choice, prices and service.

I tend to go for the Motobatt baterry as it has two sets of terminals making it much easier to connect anything additional directly to the battery without having to try to get everything under one terminal such as the trickle charger lead.

I had very similar symptoms and bought a new battery. When I removed the battery I found the electrolyte was low on all cells. Filled it up with distilled water, charged it up and it was good as gold.

Still kept the new battery though, this one is now just a spare.

Developments in trying to get this solved:

1 - my digital multimeter was giving me false readings. I checked a new 9v battery and got a reading of 14.3v and a new 1.5v battery gave me a reading of 2.4v. I changed the battery in the multi-meter (ironic ehh?) and am now getting correct readings. The old Odyssey is now showing 12.3v after sitting for over a week.

2- here in the states there seems to be only 2 readily available batteries that are the correct size. One is a BMW branded battery for over $250 usd, the other is the Odyssey for $118 usd. There are few local vendors of bike batteries and those that do have them are charging shocking amounts of money. My "local" BMW dealership is over 45 minutes way and wants $250 for the battery.

I've ordered the Odyssey from Amazon, which should be delivered on Friday. Of course I'll be on a short holiday when it gets delivered. After I get the new battery installed I'll report back on whether or not the issue is solved.

Motobatt are in the US...

https://www.motobatt.us/

https://www.motobatt.us/MB51814-Motobatt-12V-Battery

BMblB wrote:Developments in trying to get this solved:

1 - my digital multimeter was giving me false readings. I checked a new 9v battery and got a reading of 14.3v and a new 1.5v battery gave me a reading of 2.4v. I changed the battery in the multi-meter (ironic ehh?) and am now getting correct readings. The old Odyssey is now showing 12.3v after sitting for over a week.

I was chasing exactly the same problem a couple of days ago. The new lithium battery I got for my R1200S had a big warning on it, that the charging system must not provide more than 15v. So, I thought I should check it to be sure - 15.4v - bummer (also old battery showing 13v, which I thought was odd). Then I re-read this thread and saw your multimeter battery issue, and wondered…. Put a new battery in the multimeter, and bingo - 14.4v.

Thanks for saving me the expense of unnecessarily buying a new regulator. Cheers.

The issue was resolved by installing a new battery. I've been riding a couple days a week for the past few weeks and it starts up every time.

I'm amazed the old Odyssey battery lasted that long. I got another Odyssey, hopefully it will last as long as its predecessor did.

I'm glad my thread saved Grip Fast the purchase of an unneeded voltage regulator.

Cheers!