Can a bad battery stop a motor that’s already running?

[Kawasaki Jimbo]

Can a bad battery stop a motor that’s already running?

I know an alternator or reg/rec fault would do that but I think my R1 is fine in that respect (to be confirmed). The Yuasa battery is just over 2 years old.

[doggone]

With a petrol engine yes, probably modern diesel car would think there was an engine sensor fault too.
On one of my bikes it manifested as sudden stop though it was only ticking over as I'd got off to close a gate.
It would start and run with jump leads to a good battery then stop as soon as leads were disconnected.
New battery time it was nine years old though.

[Kawasaki Jimbo]

Thank goodness for the RAC who hauled it and me home on the back of a truck when the bike died on the morning commute. My phone battery was on 5% (fool!) and quickly died too after I’d called them, listened to the automated advice, received a link to their app and put in my details.

[Kawasaki Jimbo]

[stinkwheel]

Yes. I left the ignition on on my trials bike with it parked up which drained the battery. There was JUST enough life left in the battery to get it to fire up on the kickstart but increasing the revs above a fast idle killed the motor. Battery was knackered so any power the alternator was putting out was just getting sucked up by the battery.

Happily, it appeared to be just holding its own at a fast idle (and i know for a fact, that bike needs 8v to make a viable spark so the battery was well and truly goosed). With the extremely low gearing, some fine clutch control and a little foot-paddling to get moving, I managed to limp it home at about 10-15mph.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[blurredman]

Most bikes being DC ignition, yes.

One of my bikes has a poorly battery, works fine without lights on- but if I need them for the night I have to keep rpm up whilst waiting at traffic lights. EDIT: That's just for lighting too, ontop of the 5w or whatever that is required for basic ignition. Not to mention all the crap modern bikes require power for... ie throttlebodies and sensors.
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CBT: 12/06/10, Theory: 22/09/10, Module 1: 09/11/10, Module 2: 19/01/11
Past: 1991 Honda CG125BR-J, 1992 (1980) Honda XL125S, 1996 Kawasaki GPZ500S, 1979 MZ TS150.
Current: 1973 MZ ES250/2 - 18k, 1979 Suzuki TS185ER - 10k, 1981 Honda CX500B - 91k, 1987 MZ ETZ250 (295cc) - 40k, 1989 MZ ETZ251 - 50k.

[stinkwheel]

A few companies make reg/recs with built in capacitors. These will allow a bike to run with a dead or even missing battery as long as you can get it fired up initially.

You might struggle to start more modern bikes that require a certain base voltage to power up the electronics and fuel pump for the injectors. If you can get them running (in that case usually requiring a jump or a long bump start), they stay running.

We did this with a mates tiger sport. After a whole lot of faffing with a jump start pack and having it die as soon as you disconnected it due to the terminally fucked battery*, we fitted a capacitor across the battery (I carried one on my bullet road bike after the afore-mentioned trials bike incident). Bike fired up and kept running all the way home.

I fitted a capacitor equipped reg/rec to my bike after that, made by Sparx but Boyer and Lucas also make one. I still carry the capacitor because it's small in case someone else needs it.

*Turns out the battery had been on the way out for a long time and he'd been starting the bike on his jump pack for about a fortnight, this was the day he'd finally sucked every last bit of juice out of it.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Kawasaki Jimbo]

The posh fuse holder (between reg/rec and direct battery terminal connection) I fitted explicitly to warn me of such impending events before other bits were destroyed (after last time) failed by simply melting, which was the immediate cause of the breakdown. It must have let more current past than the 30 amp fuse itself. Useless! Now need to check the connectors and work out what caused the excess heat.

https://i.postimg.cc/mrHKPtWv/IMG-1460.jpg

https://i.postimg.cc/FRX83N97/IMG-1461.jpg

[stinkwheel]

Probably a bad connection between the fuse and terminal in the fuse holder.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Kawasaki Jimbo]

[stinkwheel]

[lingeringstin...]

That sort of depends on which era technology it is.

I thought only old bikes could be run without a battery because I used to do that with some of the kick start ones I had in my younger days. As I recall most of my off-road jobbies would work without batteries.

Then long about the 1990's most everything I had as a courier needed at least some voltage to fire up and a dead battery meant you weren't going anywhere.

But when I converted my bike to a Chonda CMX copy engine for a quadbike circa 2018 or so the cheapo CDI ignition I used (standard on pretty much all Chinky engines from 50cc on up) turned out to be a self igniting AC electronic ignition that will fire right up at the slightest provocation. Bump starts are piss easy and you can even start my bike by putting a ratchet on the alternator bolt and giving it a good heave-ho. I have been rather impressed at how good the cheapest possible modern Chinese AC leccy ignition works.

[Kawasaki Jimbo]

I think the fuse holder might have been squeezed and distorted by the seat, leading (as stinkwheel said) to arcing on one side. This part of the loom was a non-OE upgrade that I’ve run for years but on this bike the fuse holder ends up between the battery and the base of the seat. I’ve never had a problem putting the seat back on but now I notice some marks underneath. I think the fuse holder was a tight but perfect fit until I sat down.

Tomorrow I’ll just cut the fuse holder out, connect the two ends of the wire and then take some voltage readings. I’ll also dig out an old single-LED battery monitor from SparkBright that I once fitted to an inner cockpit panel. It was briefly reassuring back then, but then became too distracting. Same this time, I expect.

[stinkwheel]

You can get a small, self-powered, PCB mounted LED voltmeter with flying wires for a couple of quid.

So cheap, the last time I ordered one, they came in 5 colours and I ordered five so I could choose. Turns out the price was for five, not one so I got five packs of five colours.

No idea where I put them or I'd send you an handful.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Kawasaki Jimbo]

Fixed by snipping out the fuse holder and doing without, simply resoldering the wires together and using heat shrink tube on top. Battery and alternator tested and all good. Other wires and connectors look undamaged.

The washing line round the battery is there as a handle. It was difficult to get a grip on before.