Battery replacement

(paolad) · (paolad) **Join Date: Aug 2005** 08-16-2007, 10:18 PM

Last time I took my boat out one of my batteries was reading low causing my system to go beep crazy. Does anyone know how I can tell if my battery is bad? And how easy is it to replace it? Any info on this would be appreciated.

Thanks,
Paola

(acurtis_ttu) · (acurtis_ttu) **Join Date: May 2004** 08-17-2007, 6:26 AM

REplacing a battery is as about as easy as it gets. Pull your battery and take it to an auto parts store and haev it tested. they can tell you if it's bad or just needs to be charged. They will even pull it/ replace it for you if yoru ask.

(rodmcinnis) · (rodmcinnis) **Join Date: Sep 2002** 08-20-2007, 10:20 PM

If your engine is running and your system is beeping at you because of low voltage then it is probably your alternator that isn't working, not the batteries.

It could also be that the alternator is working fine but simply not able to provide the amount of current that you are drawing. If you are running the stereo at a high volume, have the blower on and then run a couple of ballast pumps you can easily be consuming more than the stock alternator can provide. Slow down to idle speed and now the alternator output drops considerably, the voltage drops and the system starts beeping....

Rod

(tonysdad) · (tonysdad) **Join Date: Jul 2005** 08-21-2007, 12:25 PM

It might not necessarily be the alternator...I have 2 batteries and they got drained so low that my alternator couldn't charge them (with everything off except for the engine). I tested the alt and it was fine. I put a trickle charger on the batts and now everything works fine. Try charging it and see what happens before you start replacing stuff...

(boofer) · (boofer) **Join Date: Aug 2004** 08-25-2007, 12:36 PM

Alternator output (current) does not change with engine speed.

(bdavis) · (bdavis) **Join Date: Sep 2002** 08-25-2007, 1:51 PM

An alternator will put out more amps at higher rpm's, that's why some rigs have high idle switches.

(05mobiuslsv) · (05mobiuslsv) **Join Date: Apr 2006** 08-25-2007, 2:18 PM

Alternators do not reach full output until a certain rpm.

(rodmcinnis) · (rodmcinnis) **Join Date: Sep 2002** 08-27-2007, 10:08 PM

James Saulpaw wrote:
"Alternator output (current) does not change with engine speed."

Wow, I don't know how you can possibly justify a statement like that.

Alternator output varies a lot with RPM, especially at low RPMs. Once a certain minimum RPM has been achieved the curve flattens out a lot but the difference between idle and cruising or even wakeboarding speeds is dramatic.

If you would like to see what a typical high output alternator's RPM vs AMPs output looks like take a look here:

http://www.balmar.net/PDF/Alternator%20Drawings/70-seriesdimensionaldrawing.pdf

Note that alternator RPM is typically up to twice the engine RPM.

Rod