motor eating batteries

I have a 1975 Evinrude 70 hp motor that seems to be eating batteries. I am on my fourth battery since July. I have brought them in to have them charged and been told that the batteries are bad. I got the fourth battery two days ago. When I tried to dtart the boat this morning, same thing!!! Any ideas what could be killing batteries? Any help would be appreciated.

Re: motor eating batteries

Have you checked charging?
Have you checked for leakage when engine not running?

Re: motor eating batteries

I think you have the opposite problem. The outboard is overcharging the batteries, cooking off the electrolyte and warping the plates. This doesn't take long if the charging voltage is not carefully regulated. Have the charging system checked.

Re: motor eating batteries

It looks like the 1975 70hp only has a rectifier, not a regulator. If this is the case, then you have to be very careful with your choice of battery. It is possible to retrofit a voltage regulator into the system after the rectifier, particularly since it most likely has only a 6 amp stator.

Re: motor eating batteries

I need to do the same thing. Anyone have any tips or a source for a regulator you could work into the system?

Re: motor eating batteries

I've heard that this works.
http://www.mfgsupply.com/01-090-1.html
Not sure, tho. Seems I read it hear somewhere.

Re: motor eating batteries

That motor has been around for over 30 years it isn't likely to be burninmg up a battery in 2 days assuming the system isn't defective.If I'm not mistaken if the rectifier is bad it can drain the battery when at rest. I believe with the motor operating at at least 1500 rpm will produce about 14 volts at the battery.
I think that motor has a magneto ignition ,not dependant on a battery, so the battery would run for a long time without charging, assuming you weren't running lots of accessories
all the time.
If there is a short, if you measure voltage from the positive of the battery to the unhooked positive cable, voltage will be present the the higher the resistance of the short the lower the voltage.

Re: motor eating batteries

The old non-regulated charging systems are designed to work with the 'old' type simple lead-acid batteries with a high internal leakage. Together with modern AGM/sealed batteries, they will 'overcharge', peak the voltage up to around 16 Volts. In this case however, the amperage will never be enough to 'boil' the battery, it will more likely burn out electronics and light bulbs. If using sealed/maint. free batteries or AGM's, install the regulator used on the models from late 90's/ early 20 cent.
In this case however. I more believe the batteries are getting drained out due to some faulty component, either on the engine (rectifier) or something in the boat electrical system.