Re: mariner charging problem
I'm not too familiar with these motors but looking at the manuals for these, they don't run voltage regulators? If this is your case, it uses the inherent cell voltage of the lead acid battery to "clamp" the voltage.
And yes, paralleling cells(adding a second battery) is basically paralleling the batteries internal inherent resistances which then in-turns lowers overall resistances(Resistance total of paralleled resistors Rt = 1/(1/R1+1/R2+1/R3....) which in-turn uses additional current(I = V/R) which in-turns lowers the supply voltage as the stator/mag is a current limited device obviously, so in the end, this helps to lower overall terminal voltage.
BUT first, how old is your current battery? Is this 16V at the battery post? if not, are all connection to the battery clean and good?
I think over time tho these un-regulated systems(although designed to have lower/limited current) tend to work batteries a tad bit harder and towards the end of life they are boiling batteries(16, 17, 18 volts). Basically, they break them down faster. Ya might just need/want to replace the batt. and be done.
http://www.boatingmag.com/blogs/diy/converting-your-outboards-unregulated-charging-system
Don't let this entire articular fool ya though, someone was getting a kickback by *omission. You can(i don't have your stators wiring but 99% certain) install a standard aftermarket merc rec/reg for $50 if ya care to and be good. Hook up the yellow wires of this where your current rec is hooked up(the stator wires), tie the two red wires together and to your battery[or use the male bullet of the two reds(the pic above has it done internally appears) as a remote sense wire], ground it and off to the races ya go. And ya have a tach output to boot....BONUS!!
http://www.amazon.com/Rectifier-Reg...bs_auto_1?ie=UTF8&refRID=0VH5QJND8G305PVV3Y6H
*It is however eluded too...."retails for about $100 which is much less than purchasing an OEM voltage regulator from an outboard dealer and modifying it to work on a motor"
But happen to use a scary word ...."modify"? There is no modify!!, Just understanding.
If however you have a voltage regulator, nevermind....lol, then obviously, that's most likely shot.
