Mercury 150 4S Serial Number 2B043673
I am relatively new to boating and have a question about the charging systems on my motor. My boat/battery is connected to the charger 100% of the time except when on the water. I have a three year old main wet cell battery that came with my boat when I bought it new three years ago (Interstate 27M-XHD). And I check the battery water levels at least every three months.
Jump forward a couple years and I have noticed that when I spend about 8 hours on the water my main cranking battery voltage is real low according to the smartcraft and my HDS units. Of those 8 hours on the water, my motor will run maybe 1 hours (I only have 70 hrs on my three year old motor). When I get home and plug in the charger I get only two red lights meaning it is only 40% charged. I only have 2 each HDS7 Gen 3 plotters, 8' power pole (barely gets used) and a small Jensen radio (MS30BT), and a NMEA with a point 1. 99% of the time I do not keep fish so live wells are empty and not running.
I assumed that when running the motor, the alternator charges the main battery much like an automobile does, so I try to find a stretch where I can run my motor about 4,500 rpm for a good 5-10 minutes to charge the battery. I will see a slight increase in voltage on my smartcraft (maybe .3v), but nothing like I would expect it to display if being charged like an automobile charging system.
My question:
Does the alternator on the 150 4S charge the main battery when the engine is running and if so, does it need to be a high rpm for a prolonged period of time to make any noticeable change in indicated voltage?
I realize my main battery may also be due replacement and this may not be a charging issue, at all but I wanted clarification on the alternator charging while the engine is running.
Thanks in advance.