Battery-Alternator-Voltage

Teachable Moment time:

My cousin is a car guy, runs a parts store. He knows most everything there is to know about cars. Last year he was down for a week and used my ’89 Sport. I was at work one day when he called and said my battery was not putting out enough voltage. Long story short, he bought a deep cycle marine battery and put it in the boat. He also replaced the alternator.

Today I am reading up on the forum and there are several posts saying that deep cycle marine batteries are bad. Can someone explain to me why? And should I replace it immediately?

Also, is there any difference between a car and marine alternator? The boat read 12v on the positive side of the battery, but the gauge shows around 10v. Could easily be a bad gauge since it fires right up every time, but the posts I read have me doubting myself now and thinking the alternator might be the wrong one.

Can someone school me on the topic? I am a routine maintenance kind of guy, not a mechanic.

Thanks!

I would worry more that he installed an automotive alternator than a deep cycle battery. Marine alternators also ramp up the voltage a little different than a car because of the sustained RPM's in a boat they see on a boat.

Bri892001 wrote: Do you remember what your dash gauge read before? I would just go by what voltage you get at the battery. There's a few reason's your dash gauge may read differently. Well, one main reason, and that it undersized and potentially corroded wiring/connections going to your dash and in your dash.

Seems like it always read 14 Volts.

I probably didn’t pay much attention to it after he replaced it last year. It was toward the end of the season, and the boat had new alternator/battery so I didn’t pay much attention. This year when I charged the battery and took the boat out, I noticed it reading lower than the normal 14 Volts.

I get a 14v reading at the battery. Shouldn’t I be getting 14.6V? I am not sure I should really be too concerned, but I just want to have the correct setup. (I am learning as I go and use the site to school me on the right way to do things!)

Its unlikely you ever had a charging issue in the first place. Our year boats are notorious for undersized wiring to the dash, causing a voltage drop. Put a larger load on the dash and the voltage reading will drop further (blower, lights, etc). This problem gets more obvious as time goes on, as wires and connections corrode. To really fix the issue, you should clean your connections, replace any worn out breakers, and run extra power and ground wires from the engine to the dash.

I would put the original alternator back on. If its gone, then make sure what you have on there now is rated for marine use- its a safety issue. Marine electrical components (distributor, starter, alt) need to have spark suppression built into them to prevent the ignition of gas fumes in an enclosed space.

I would also ditch the deep cycle battery. Theyre meant for trolling motors and large stereos (small current draw over a long period of time). You dont need a marine battery for our boats- a good starting battery (large current draw over a short amount of time) works best. A Group 65 battery fits in the battery box nicely.

ha ya cousins what do they know? Seems like the only thing I ever learned from cousins is what not to do by their bad examples.

8122pbrainard wrote: The cousin doesn't by chance have a Autozone franchise does he?

Oh Pete, you stole that one from me, I almost made that comment but thought it was below the belt.

Give me a cousin who spends his own money to fix something (even if done wrong) over the little brother who leaves it on E every time he uses the boat!

...and no, it is Advanced, not Autozone.