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Author Topic:   Battery Problems
wjriling posted 07-24-2003 09:26 AM ET (US)   Profile for wjriling   Send Email to wjriling  

I bought a Mercury 25hp classic last August with electric start. After being stored in my garage all winter the battery needed to be recharged. Took the boat out for a few hour yesterday and while the electric start worked perfectly when we headed out, a few hours later the battery was dead as a doornail. Should the battery have been recharging while the motor was running? I'd hate to think that I will have to buy a new battery every year.

Any thoughts or suggestions would be greatly appreciated.


Dick posted 07-24-2003 10:18 AM ET (US)     Profile for Dick  Send Email to Dick     

The Merc 25 has a 6 amp charging system which should keep a good battery alive. I would take the battery back to where you bought it and have it load tested. If it is an inexpensive auto battery replace it, I prefer the Interstate SRM-24. I sell several hundred a year and have no problems.


wjriling posted 07-24-2003 10:30 AM ET (US)     Profile for wjriling  Send Email to wjriling     
Thanks Dick. I am actually using a 12 volt Marine Starting battery from Midstate Battery (The battery came with my engine set up). After reading your post I called Midstate and they said they would be happy to load test it. Can I assume if the battery is fine that it my be the charging system on the motor that is causing the problem?

Thanks for your help.

triblet posted 07-24-2003 10:42 AM ET (US)     Profile for triblet  Send Email to triblet     
Sitting all winter without a charger is NOT good for the
battery. It will very slowly self discharge itself to dead
flat, and dead flat is real bad for lead acid batteries.

It's cheaper to buy a Schumacher smart trickle charger and
leave the battery on that all winter (and summer too while
it's out of the water) than to buy one new battery. My
occasionally driven Corvette has been on one for over ten
years. Same battery.


Wet Foot posted 07-24-2003 11:02 AM ET (US)     Profile for Wet Foot  Send Email to Wet Foot     
Should the electrical cables/wires be removed from the battery before charging? It would be easier for me to leave the battery in the boat and the cables on. I was told by my dealer to remove cables and pull battery out of boat before charging...a job in itself. Also, my charger instructions show jumper cables on the battery, and the charger clamps on the if it's dangerous to locate the charger too close to the battery...necessary? If your battery gets fully discharged and is recharged, should I replace it in the near future, or will it still have a long dependable life? Input appreciated!
Tom2697 posted 07-24-2003 03:03 PM ET (US)     Profile for Tom2697  Send Email to Tom2697     
At 6 amps, you will need to run the motor for a 10 hour period (give or take) to get a decent charge on your battery. This is running at speed, without turning your motor off and restarting, no radio or other electronics, etc. I thought my batteries were dead. Fortunately, my new motor puts out about 40 amps ('03 suzuki 140 4-s => am I correct in this?) and charges the batteries up well.

My recommendation, have the battery load tested and then recharge it (via a charger) overnight if it is okay.

Question: how many accessories do you have connected to the battery? Lights, VHF, sounder, stereo, etc....These can easily draw more current than your alternator can put out and thus, you will be draining your batteries everytime you use your boat. You then have three options: (1) don't use all accessories at the same time; (2) make certain that you charge your battery fully before you go out; or (3) bring an extra battery with you. I did all three until I bought the new motor.

JohnJ80 posted 07-24-2003 08:01 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
If your battery is discharged without charging for a long time after it is discharged, the battery chemistry starts to change. The sulpheric asic and the Lead combine to form lead sulfate which ultimately shorts out the plates and kills the battery.

every time you leave one discharged like this you damage the battery.

When you recharge a battery after discharging (soon) you put the Sulphuric Acid and Lead back into a 'new' state and reverse the conditions that lead to the lead sulphate forming.

So, it is important to never let a discharged battery lie for long.

If you have left your battery discharged for a long time, you may show that it is a good battery (voltage) but it will not have the current capacity because, I think, the sulfate forms on the plates but hasn't shorted them out yet. If the sulfate has built up along the bottom of the plates, you will see the battery voltage drop and you won't be able to bring it back - it will never get above 12V.

The only way to determine the current capacity of the battery in the first case is to have it load tested and see how much current it can supply for what period of time. If you can't get the battery voltage up to 12V and have it stay there, then you have a dead cell and it needs to be replaced.

You can charge your battery while it is connected to the boat with no problem. However, you should not try to start your boat or run the accessories. If you did this, and if you battery were unable to supply the current (perhaps because it is damaged) the charger would be called upon to provide the current. Depending on how good a charger you have this could be no problem or it could be dangerous if the charger had no current limiting capability (most do). It is too much of a hassle to disconnect the battery, I would just charge it there with a good charger and be careful.


acseatsri posted 07-24-2003 09:30 PM ET (US)     Profile for acseatsri  Send Email to acseatsri     
I have a 2-battery setup on my outrage- only a 9-amp charging circuit on the engine. I work with it by leaving the switch on "both" batteries when I'm running to or from a destination, then switch to 1 battery when I'm at anchor or idling with the electronics or lights on. That way I always have a fully-charged starting battery.

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