Low Battery Alert on VHF and readings from batteries

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Island Dreamer

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Took my boat out for the first big trip with the fam today and did about 60 miles round trip going to Anacapa and Santa Cruz Island. I'm concerned about my two AGM batteries being weak or if the alternator is going out. I'm really not well educated with electrical issues but can use a multimeter for a few things.
The VHF flashed a low battery during the 8 hours that I ran the boat today. She started ok but the first couple of cranks sound slow and speed up and get more powerful with each turn of the Volvo 5.7. The volt meter gauge on the boat was showing 12.5V at 3000 rpm while running. At idle, one battery showed 11.8 volts and the other 13.8 volts with the battery selector positioned at "both".
Can anyone tell me if I should first replace the batteries or change the alternator. The only reference point I have is that the gauge on my Dodge diesel truck is at 14v when its running so maybe the alternator is not putting out the right amount on the boat? Not sure how to explain two different charges in the battery.
 

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The 13.8V says it's charging......Now The first thing that needs to be done....and in this order.
Charge both batteries independently. Then have them Load tested.

A Batt. switch like a Perko in Both is not a Great thing. This is why I push a BEP Cluster.

Think about installing one....Only then will you have a dedicated House battery. What you have now is a Start battery as to which one is connected.

If one of your batteries is good...and one is Bad.....and you combine them...IE: The Good one will discharge trying to bring the Bad one up....and then you get 2 dead batteries.

The next step is to remove / inspect / Clean all Battery connections.

I see cables on peoples boats all the time that are Junk.
 
What he said...

Particularly about checking the connections to make sure they are meticulous and tight. I also highly recommend getting a system to isolate your starting battery from your house battery. BEP is just one maker, but the concept is the same and not very expensive given the peace of mind it provides.
 
First off, I agree with all that Warthog recommended.
I had the exact same problem on my 2520 (Yammi powered) 2 years ago. Found that one batt was getting charged properly. Swapped in a new batt, but same issue. I dug into it in the off season. Found one of the cables for the port batt that runs under/along the transom had a razor cut in the casing that had corroded over the years. It must have been since build being that the damage was in a blind spot that was only viewable once the cables were removed. Installed all new cables along with BEP cluster & no problems since.
 
iltfish said:
First off, I agree with all that Warthog recommended.
I had the exact same problem on my 2520 (Yammi powered) 2 years ago. Found that one batt was not getting charged properly. Swapped in a new batt, but same issue. I dug into it in the off season. Found one of the cables for the port batt that runs under/along the transom had a razor cut in the casing that had corroded over the years. It must have been since build being that the damage was in a blind spot that was only viewable once the cables were removed. Installed all new cables along with BEP cluster & no problems since.
Click to expand...
 
I'm going to pull both batteries and hook them up to a charger and do what you recommend. Is 12.5 on the gauge normal for batteries that might not be in good condition? With two new batteries would the gauge read higher while underway?
 
Full charge is 12.6 volts. When underway and being charged by engine it can be as high as 14 volts. After you charge the batteries they should rest at least 30 minutes before you do a load test.
 
As Knotflying said.......Each cell will give you 2.1volt......12V battery has 6 cells. 6 X 2.1 = 12.6V for a fully charged battery....If you have one at 12.5.....Call it good as to a full charge. But Get it Load tested....That will show if it good or not.

As to the reading while underway and engine above 2000RPM...

There is a variance as to output that is acceptable. 13.8V to 14.2V is in the norm range.

It can vary between volt meters and how good the connections are.
 
love my harborfreight loadtester. Have eight boats that are used in a club/school setting and all kinds of lack of understanding from operators. Load tester gives me huge peace of mind. Battery shed is a 1/4 mile from water so helps bigly when I know I have a good battery
 
Do not know if I am missing a thread but there could always be a discussion on battery care and maintenance. I store mine on trickle maintainers after fully charging and load testing. I run a couple of desulfate cycles through the fleet during the winter months. I keep a 1/2 x 9/16 open end combo on a float and have painted all the positive 5/16 posts red and the 3/8 posts yellow. Probably old school but all of the batts are stored out of the boats on wood racks. No contact with concrete or the ground
 
Actually on the subject of sitting on the ground.

I've never heard anything about "Glass Cells".

But earlier than the '50's.....thru the '50's and into the 60's....The case material had to do with that....Those days have been long gone....But that is where that started.

I have a Gp24 deep cycle sitting in the dirt right now. It is hooked to a solar charger. Works great.

I have several batteries sitting on the concrete in my shop.....I just charge them every couple of months, or when I get around to it.
 
All good info. Can someone please explain the BEP cluster? Please forgive my ignorance. I’ve always used a switch for ‘off, 1, 2 or both’.

Always open to upgrading and improving.

Cheers
 
Island Dreamer, check your batteries as others said. I have the 5.7 and above 1,000 rpm you should have full alternator output. The voltmeter on the instrument panel is not precise but effective. Mine usually reads about 14.2 volts. One of my depth sounders has a voltage screen that I can double check with.

You might have a failing battery.

Dana
 
Update- 3 days after running the motor for 8 hours, I found one battery to be at 12.5 volts an the other at 11.5V and this was with the isolator turned off during the three days. I charged the battery overnight on a good chargerwith an AGM function since these are Optima Blue top marine batteries. It was at 100% the next morning. Took it to AutoZone where they load tested it and after said it was at 74% so they are replacing it for free. Might take the other one in also in hopes of having getting it warrantied if there is an issue. Once I get both batteries back in I will check the VHF and report back. Side note....what a pain in the rear it was to try and reach down and life that thing out! A strap will help next time.
 
One battery was replaced under warranty today at AutoZone. The other one at 12.5 was last run 8 days ago for 10 hours and had 12.5 volts but under load test hit 60%. Employee said it was in range of begin good but would exchange it for a new one if I wanted.
 
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