How to charge battery from a car?

[iandunn]

I'm pretty sure I drained the battery trying to start my '90 GS500. I'm thinking about buying the Battery Tender Jr. to charge it, but can I just charge it from my car? If so, what's the procedure (I know I shouldn't start the car engine, but should i turn the car on?)? Or, is it worth it to get the tender for the winter (keep in mind I'm a poor college student. Er, a cheap, poor college student ). I also found a Diehard charger that's only $5 more (and I wouldn't have to wait for shipping). Is it a better charger?

[Kerry]

Some observations:

* The

DieHard charger is likely to have larger clamps, so they will fit over car battery terminals.  The Battery Tender Jr will have smaller clamps that fit into the "recess" around the GS battery better.

* The cable coming from the Battery Tender Jr is actually a 2-part job.  You normally leave the end with clamps attached.  BUT!  the secondary cable that comes with the unit can be permanaently attached to the battery, with the modular plug left hanging (or tucked away) somewhere that you can get at it.  In the winter it would be nice to pull into your garage (or whatever), plug the Battery Tender Jr into your bike, and forget about it till your next ride.

* The DieHard unit weighs 2.5 pounds.  The full-blown Battery Tender weighs 2.7 pounds.  The Battery Tender Jr weighs ONE pound.[/list:u]My opinion?  If you need a charger that can handle the car battery go with the DieHard.  For bike only, the BTJ is the one.  

[TheGoodGuy]

i have a sears 10/2Amp charger.. works for the car and the bike. When i charge the bike its on 2amp mode, when its on the car (if i ever need to) it will go on the 10amp mode.

I rather have a proper charger than a thing that trickle charges.. in my case im not sure if the sears charger will trickle below 2amps, but i assume it would.

[se7enty7]

I paid $20 for a charger from walmart.  it does 2 amps, 6A and 20A.  I will be riding mine enough to not need to trickle charge it.  The charger stops charging at a certain voltage (14.5?) and will start again if battery goes below 12ish.. (dunno about the voltage figures... just guessing here.)

[pantablo]

I will be riding mine enough to not need to trickle charge it.  

me too.

[iandunn]

Can I just charge it with my car, though?

[se7enty7]

Can I just charge it with my car, though?

Start it? Yes.  Do it with the car not running.

Charge it?  I wouldn't.  I'm about as broke as they get (college student in atlanta... ) and I dished out $20 for the charger.  It's a good investment considering a battery is $65+

[Rema1000]

When connected to the car, the battery will charge (in Amps) proportionally to the difference in voltage.  With a sufficiently dead bike battery (<11v), and a running car (14.8+ v), that will cause way too much heat in your bike battery. The plates inside will warp, and short a cell (that's bad).  Connecting the car battery (with the car engine shut-off) directly to your bike battery will likewise charge it, and not quite so fast... but still too fast.  

It's much better to jump-start the battery from a car, then ride the bike on the highway to charge it.

If you are interested in D-I-Y battery chargers, I have used a lightbulb as a variable resistor to limit the current from a large 12v source (like a car battery), to make a trickle charger.  Google on "trickle charge lightbulb"; for example, see http://www.alpharubicon.com/elect/3dollarbattggn.htm for a related use.

[jkstyle834]

yea... i just bought my battery charger with the clamps that stays there permantly... pretty good.. i think mine charges at like 1amp?? real slow... but it's better for the battery they said...

[iandunn]

I ordered the Battery Tender Jr., thanks for the help

[jamesmcb]

If you just start it and leave it idling for a while every couple weeks will it keep a charge?

[Rema1000]

If you just start it and leave it idling for a while every couple weeks will it keep a charge?

Probably not.  Put a voltmeter on it while it's idling; if the voltage is (say) 14.5v, then you can (mostly) charge on idle.  On my GS, I only get 13.8v at idle, which will cause a very slow charge at idle, and the battery will never reach gassing voltage, so it will never completely charge-up.  It would charge part-way, and not terribly quickly at that.

On my bike, it is necessary to get the RPMs above 5k or so to get the voltage into 14.5-14.8v, which is a good range to charge at.  The exact behavior of your bike depends on the health of your Regulator/Rectifier.  They vary quite a bit, and their behavior changes over time.