Battery goes flat when it rains

J.M. · World Chat Champion Joined: 27 Mar 2011 Karma :

So I've had this bike for a while now and I usually have no troubles starting it. I usually keep it in a dry place where the rain doesn't get to it.

I've noticed that it sometimes runs out of battery though and the common thing throughout this seems to be the rain.

For instance, I went over to my girlfriends once who is 160 miles away a while ago. The bike started a treat before I left. I rode the entire way there only stopping at one petrol station about 140 miles in. Bike started lovely after filling up (which it should as the engine is still hot) and I finished off the rest of the journey.

Once at hers, it started raining for the entire weekend. On the Sunday evening, I attempt to leave (arrived Saturday afternoon) and the bike won't start. The battery is flat. I managed to bump start it and away I went. From there on there was plenty of charge in the battery to let me start the bike effortlessly when stopping at petrol stations and service stations.

So that rules out an alternator fault because the battery is being charged.

It's also happened again today. I'm supposed to be at college right now but instead I'm sitting here typing this whilst the battery is on charge.

Last night I went out for a ride. Battery was a little bit flat but just enough to start the engine. I did about 40 miles without stopping, just thankful to finally be out and about on my bike again. I got home and couldn't be bothered to put the bike away. I was tired and my shed was a complete mess, so I would have to tidy up first.

I just left it on the driveway.

It's been raining this morning. Not excessively heavily, but trying to start the bike just didn't work. Flat battery again.

This never seems to happen when the bike has been left in the dry. It only seems to happen when the bike has been left out in the rain.

Any ideas why? I'm stumped.

I don't think it's the battery because it's been kept off the road for a month whilst I fixed it and it started perfectly going out on it last night. So the battery holds charge alright.

My usual commute is 10 miles and I always seem to have a fully charged battery at both ends. At college the bike is kept under a shelter where it's pretty dry.
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2004 R1 & 2018 XSR900

pinkyfloyd · Super Spammer Joined: 20 Jul 2010 Karma :

Not big on bike repairs but first thing I would do is check your wiring, especially around the connections, lights, fusebox ect. Possibly the rain creating a circuit between the positive and negative connections and draining the battery.
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J.M. · World Chat Champion Joined: 27 Mar 2011 Karma :

Could a connection between the positive terminal on the battery and the frame cause this?

If so it could be the heated grips that the previous owner installed. I'll wrap some electrical tape around that connector now to be safe.
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2004 R1 & 2018 XSR900

map · Mr Calendar Joined: 14 Jun 2004 Karma :

Suspect a leak to earth. Check the earth strap and earth connection from the battery to frame. One I had recently looked ok but just crumpled to dust when actually felt.

Other than that it maybe a short in the wiring leaking to earth when damp or indeed the extra heated grips (check any switch in circuit).

HTH Thumbs Up

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mysterious_rider · World Chat Champion Joined: 11 Sep 2010 Karma :

MarJay · But it's British! Joined: 15 Sep 2003 Karma :

J.M. · World Chat Champion Joined: 27 Mar 2011 Karma :

I've just been out to the bike with an umbrella and wrapped the suspect connections connecting to the battery with electrical tape, leaving enough to still connect them to the battery though.

The heated grips (+) 12v to the relay had a about 5mm of exposed wire where the previous owner had obviously stripped too much of the wire when attaching it to the circular terminal to the battery. This wire (and exposed part) ran extremely close to the frame, so with moist I suspect that a circuit could be created between that and the frame. Though the wires all looked and felt dry when I removed the seat earlier.

P.addy · Red Rocket Joined: 14 Feb 2008 Karma :

IIRC your lights come on with the ON ignition position.

Try starting straight away to prevent draining, I've started the bandit on 12.1v when I got the new battery. It started ok...bit slow on the starter though.

LOL at bump start, in damp, before IOW ferry. Fun Laughing

J.M. · World Chat Champion Joined: 27 Mar 2011 Karma :

Yep, they do.

If I use the Cyclone's electric start though, that seems to be better at starting the bike on low battery than using the starter button itself. Just don't have the Cyclone connected at the moment so it wasn't really an option.

I hate the GS when it's cold. It's a right pain to start. Had about 12.5v in the battery and tried to start it. Almost got there but the battery gave up before then.

I just gave up in the end now. Battery is on charge in my room. I'll leave it on charge overnight and fire her up in the morning. Successfully, I hope.

Yeah, that was an interesting start to the morning Laughing

See what I mean though. It started perfectly the rest of the day and the day after. Thinking

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2004 R1 & 2018 XSR900