Hello all,
I have an outboard engine that I want to understand. It is a Mariner 40hp 1988 model, and it is operating just fine. At least I think it is.
The only little thing I am not completely sure of, is I noticed a rapid increase in temperature on the starting batterys negative / ground pole after repeated starting attempts.
Background:
I had used the battery (Exide Start / Stop branded) to run a bilge pump, and had to recharge it before starting the outboard. I noticed the starter motor had trouble turning the flywheel, but after several attempts where the flywheel would ony turn once pr. attempt, outboard did start as normal. Then I disconnected the battery to move outboard, and noticed the negative / ground pole and wire connected to the battery was very hot. Maybe 40-50 degrees Censius.
I then did a test on the battery itself, and found it was just vbarely above 12vdc (12.3v). I hooked up the charger again, and after some 20 minutes the charger felt the battery was full. Voltage on battery was 12.6v, and when attempting to start outboard again same thing happened. Starter motor would only turn flywheel a couple of times, and then only barely one turn pr starting attempt. Negative was hot as before.
I gathered I had ruined the battery by using it to run the bilge pump (overdischarged it), but since I could not completely rule out faulty charger I went and bought a new starting battery and a better charger with a separate "Desulfication mode" / "Repair mode".
New battery took some ten hours to charge fully with new charger. New charger did not perform any different on the old battery. When I set it to "repair" mode, it quickly exited that mode and went into regular charging mode, but displayed an icon indicating it was charging a motorcycle battery (!). I would also do the "motorcycle thing" if set to "automatic mode", but if set manually to "car battery mode" it would stay there and claim battery was fully charged after some 10 minutes (still only 12.5 - 12.8v on the battery).
Now. I dont plan on using the Mariner 40hp as I have a 70hp Johnson. My new battery spins the 70hp Johnsons flywheel like it was paper. I am curious if the new battery will spin the Mariner as well, but I am unsure if it was indeed the Bilge-pump that destrøyed the old battery or if there is something wrong with the Mariner.
Question:
Is there a common condition where a circuit (that could possibly be embedded in the Mariner) would build up heat like described above on negative side of battery that can destroy a battery?
How likely is it that I will ruin the new battery if I try to use it to start the Mariner? Is there a test I can do (simple) on the negative or positive side on the mariner to rule out a potentially "batterydestructive" error?
Sorry if this is a stupid problem. Batteries are so expensive, and I dont want to ruin the brand new one