My bike was dead this morning...

[Crazy_Canuck]

I went out to my bike this morning to head out to work and the battery was totally dead. Looked at the ignition and it was still in the on position, I guess I did not turn it off when I got home from work yesterday I tried to jump it with one of those battery packs but it did not have enough power to turn over my bike

 

I am going to go home at lunch to see if I can jump it with my truck.

 

Question: Is the battery still going to be OK?

[smiller]

It's not exactly good for it but it should survive (and if it is an Oydessy or other AGM battery then better still as they will be less affected by this type of abuse.) Only way to know for sure is to give it a full charge (best to use a good charger for this vs. jumping the bike) and see how it performs going forward.

[lubie]

i would recommend taking the battery out and charging it. can be hard on an alternator to charge it if it's dead. may not hurt, but it's easy to pull the battery.

[Ken H.]

can be hard on an alternator to charge it if it's dead

How? Alternators don't have a duty cycle limit that I've ever heard of.

[black99S]

can be hard on an alternator to charge it if it's dead

How? Alternators don't have a duty cycle limit that I've ever heard of.

Alternators have an AMP-RPM curve that starts with very little Amps at idle and increases to near maximum at ~4000RPM. Unless you plan to jump start your bike and RIDE you will not get a good charge - idling the bike will do very little but overheat your bike and leave the battery partly charged and sulfating. Jump start at the battery terminals and not through the accessory outlet - you may melt the wire insulation.

 

You are better off to use a good 3-stage battery charger sized correctly to fully recover your battery. C/20 rate is recommended with C/10 the maximum. C is capacity in Amp-hr, so for a 40A-hr battery 40/20 = 2-Amp charger is optimal and 4-Amp is maximum. Too high a charge rate will overheat and damage your battery too.

[smiller]

I would agree that using a charger to bring back a dead battery is the best choice, but only because a proper 3-stage charge would be better for the battery under these circumstances (and check the battery manufacturer's recommendations for the recharge because sometimes something other than a C10/C20 rate is recommended, as in the case for the Odyssey for instance.)

 

But beyond that, while recharging a dead battery by normal operation the bike may not be the best way to do it I can't see why one would worry about it hurting the alternator, especially the relatively large one on a BMW. If that's the only method you have available, go for it.

[Crazy_Canuck]

Thanks for the info guys.

 

I went back home on my lunch break and I jump started it then rode it to work, I dont know if that was enough to charge it. I will find out when I try to go home today. If it was not enough I will jump one more time for the ride home and then put the battery on a charger.

[drodg]

Is it okay to jump from a car or truck? Thanks

[smiller]

Is it okay to jump from a car or truck? Thanks

Although it is done personally I wouldn't. When you connect a car battery to a small, discharged motorcycle battery a lot of current will flow, probably much more than the smaller battery is designed to accept. The worst-case consequences of this can be pretty nasty.

[Paul Mihalka]

Is it okay to jump from a car or truck? Thanks

Although it is done personally I wouldn't. When you connect a car battery to a small, discharged motorcycle battery a lot of current will flow, probably much more than the smaller battery is designed to accept. The worst-case consequences of this can be pretty nasty.

I am curious about this statement. First step: You connect a large fully charged (12.6volt?) battery to a fully discharged small battery. Is there any significant current flow? If you would now disconnect everything without adding charge from a charger or alternator, would the previously dead battery have some charge? I don't think so. OTOH, you connect the charged big battery to the dead battery and jump-start the bike, the current flow will be from the charged battery directly to the starter and motor of the jumped bike. If you would shut everything down now, disconnecting and stopping the motor, the dead battery would still be dead. What am I missing?

[smiller]

First step: You connect a large fully charged (12.6volt?) battery to a fully discharged small battery. Is there any significant current flow?

Normally, yes.

 

If you would now disconnect everything without adding charge from a charger or alternator, would the previously dead battery have some charge?

The car battery would act the same as a very high-capacity battery charger so yes, the weaker battery would probably have some charge, depending on how long you had them connected.

 

OTOH, you connect the charged big battery to the dead battery and jump-start the bike, the current flow will be from the charged battery directly to the starter and motor of the jumped bike.

A lot of the current would indeed be drawn by the starter motor (lower resistance than the battery), and for that reason if you want to try jumping this way I'd get on the starter very quickly after you connected the two batteries and disconnect them immediately after the start.

 

This concern is less critical when jumping car-to-car because a car battery can absorb a lot more current without overheating than can a small motorcycle battery. In the latter case, if you get on the starter right away and then disconnect the jump battery right away after the start (meaning you don't give the small battery time to get cooked by the large battery) then maybe/probably the procedure could be acceptably safe, but personally I would avoid the attempt unless I had no other option.

[ShovelStrokeEd]

Internal resistance of a typical motorcycle battery is about 2 ohms. 12.6 volt charge on the car battery, 6.3 amps worth of current flowing into that leetle battery that is inside a box with no good place to reject heat. Not a good thing.

[smiller]

Your thought is correct but one value is off, the internal resistance of a typical lead-acid battery is more like fractions of an ohm, not 2 ohms. A 6-amp charge rate wouldn't be such a worry, the problem is that one could easily see 20-60 amps flow into that little battery under the right (or wrong) circumstances. One can draw their own conclusions as to the safety of such an event.

[DrDakar]

Same thing happened to my battery last week. Totally dead. I charged it 10 hours, now it is working. I think I can use it for a couple more months.