Last weekend, first time I got to go on a significant ride on my recently-fixed GS, it wouldn't start after an hour long ride. Battery was dead, or mostly dead. I wouldn't have been surprised if the battery was low after getting the bike back from a month-long stay in the shop, but one would think an hour long ride would be enough to charge it fully. I could have sworn I read somewhere on GStwin.com that these bikes don't really like to charge the battery under about 4K rpm. Is that correct?

FWIW I charged it and rode again several times since then including a couple of additional longer rides, several 30-45 minutes or more, all of which I made an effort to keep the revs above about 4K while cruising. So far it's starting fine. I just hate to risk getting stranded.

Hey mr72, I've had an experience just recently with a bit of battery weirdness. I'm sure others here will be able to add to, or argue with, this post.

I say weirdness simply because it was never enough to stop the bike from starting. I live in a very mild climate and my bike usually starts from 'cold' with just the gentlest, minimal press on the starter button with the choke on full. A while ago it was taking two attempts to start it. I'm sure most people wouldn't even consider this a problem, for me it was an unexplained change in behaviour - weird.

Two things working in concert contributed to the weirdness. First, the after-market battery I installed a year ago has the vent on the left rather than the right hand side. Not really a problem, a short length of tubing and it fitted. The vent is on the earth / negative / cathode side of the battery. Second, I've been told by a source I trust that the cell nearest cathode is a wet acid battery tends to vent water vapour faster than the other cells in the battery. On this battery the left hand cell vents faster and has easiest access to the vent tube - hence greater evaporation.

These two elements conspired to create the situation where the cell on the left hand side was low on fluid. Although the bike was putting out 14.4 ish volts at 3000rpm the battery wasn't effectively capturing the charge.  I topped up the battery, gave it 24 hours on a reasonably 'smart' charger - problem solved.

I have read the same thing.  The batter will only charge around 4kish.  I can't confirm or deny this,  but I will say that most of my trips are short commuter trips to work and back of a few miles and it's all slow speed zones where my RPMs stay below 4k.  Luckily I haven't had a problem thus far.  4k RPMs in 6th translates to about 50 miles per hour and the areas I ride through the week to and from work are all 25-45.  I suppose if i were to become an issue,  a person could always just ride in a lower gear that would achieve 4k during short commutes at lower speeds to ensure charging takes place.  Anyone else want to chime in on that assumption?

Here's what the service manual says:

Fully charge the battery and load test it.

Quote from: sledge on November 16, 2016, 03:26:53 AM
Fully charge the battery and load test it.

I have to agree with sledge here. Make sure the battery is actually holding a charge before you try to diagnose a charging problem.

As some of you may have read in my thread a while back, I recently left my key in my bike in the "on" position and completely drained my battery. I jumped it enough to start, but it died while idling. The only time that the bike wouldn't die was if I kept the RPMs up in a higher range (don't remember exact numbers though).

This seems to support the idea that the charging system only really kicks in at >4K RPMs. However, before you worry about the charging system, you should ensure that the battery itself isn't the cause of the problem. Usually batteries go bad much sooner than the charging system.

Yeah thanks for the input. The battery is nearly new and it absolutely holds a charge, pretty sure that's not the problem.

I'll do the charging system check. I have a lot of electrical work to do on the bike anyway.

Also agree with ya on the month long stay at the shop.  probably had a ton of cranks during diagnosis and trouble shooting and testing at the end. Maybe left it in a weak condition.   My new battery was flat after just an hour or two  with the key accidentally left on.  a good charge over night on trickle and it hasn't failed me since.  Topped it off with some distilled as well.   But never hurts to run a meter over it. 

Yep, I figured the month long shop stay was most of the problem, coupled with the fact that when I picked it up, they started it just to move it out front like 50 feet, then started it when I got there in the parking lot to demonstrate that it was in fact running, shut it off immediately, then I started it again and shut it off right away before starting it and riding it home 1.5 miles. That's a lot of starting with no charging. I am guessing that, coupled with the long ride with the light on but not enough revs to charge, really left the battery flat.

I notice the charging system check calls for running it at 5K rpms. Can anyone confirm that it really does not charge sufficiently, by design, at <4K rpms? I can always measure the voltage while it's running at idle or 2K rpm but the question is whether that's an indicator of a fault or normal operation.

I believe the GS500 starts charging at about 2000 rpm depending on demand.  Here's an old thread on the subject:

http://gstwins.com/gsboard/index.php?topic=40477.msg454644

Quote from: gsJack on November 16, 2016, 01:44:11 PM
I believe the GS500 starts charging at about 2000 rpm depending on demand.  Here's an old thread on the subject:

http://gstwins.com/gsboard/index.php?topic=40477.msg454644

Thanks for that. Good stuff in there.

thanks Jack.  great info as always.  appreciate your insight and replies.

Well it wouldn't start again today after ~120 miles of riding, probably started 10 times. I was persistent in running it at >4K.

Weekend, will check the charging system. Thanks for the info guys. I think yet another thing may be broken on my GS.

Fully charge then load test the battery. Its the weakest most unreliable part of the charging system, assume nothing!!

Static voltages mean very little, its the batteries ability to deliver current when subject to load and voltage drop that matters.

Yes.....the problem could be further up the line but a duff battery can confuse dynamic test figures and make it look like the reg/rect is faulty. It has to be checked, if only to rule it out.

I use one of these, its an invaluable piece of kit.

http://www.drapertools.com/product/53090/100Amp%20Battery%20Load%20Tester

Great info sledge. thank you.

I haven't load-tested it yet or checked out the charging system due to a lack of time today.. but! I did charge it overnight and the battery has me a bit mystified. It's been at 13.6 volts for 6 hours since pulling it off of the charger. I haven't measured it when it's 'dead', but if it's much over 12.5 volts then I can see why the GS has a tough time charging it. If my bike's charging system is on the low side of normal, then it may not produce enough voltage to charge that 13+ volt battery consistently unless it's really revving.

Google for...deep cycle faults and......sulfation. See if the symptoms match up.

A difficulty in accepting and holding a charge does not necessarily mean the generator or reg/rect is faulty and the test procedures all assume the battery is healthy.

Just because the battery looks new means nothing, it could have been left uncharged for a year before you got your hands on it........... you just don't know 

Last time of saying.........."Take it to a shop and get it load tested"...... most places do it FOC. If it comes back good move on to the reg/rect and the stator ........otherwise you could be wasting time, possibly money chasing non existent faults!!

Josh, you can take the battery to Auto zone or wherever - they all can do a load test on it.

I agree with Sledge.  The battery is also the easiest and probably cheapest component to replace and eliminate from the troubleshooting process. They are not designed for full discharge/recharge (unless it is a deep cycle battery) and will nosedive quickly if that happens.

Yeah I wish it was the battery. When I said it's almost new I didn't mean I think it looks new. I have the receipt from the previous owner. It's pretty much new. And it also tests good. I took it over and had it load tested.

I am still mystified as to how a fully-charged 13.6v battery can be charged by a system rated only at 13.5 volts. I'll do the test charging system test tomorrow.

The PO did replace the regulator/rectifier unnecessarily while trying to sort out an ignition problem, and I have a spare. Also he did a lot of questionable wiring mods, which I intend to undo. So it's entirely possible there is some wiring problem or the regulator/rectifier needs to be replaced. Just have to check everything out.