Diagnosing an electrical issue

[Epenn]

My engine will not crank, and other electrical appliances are weak. When I use a car jumper kit, the engine starts up right away as usual. I took the following volt meter readings directly from the battery terminals:

- Battery charger off, engine off ~9.7
- Battery charger on, engine off ~13.5
- battery charger off, engine on ~ 9.7
- battery charger off, engine running for an hour ~9.9
- battery charger off, after engine turned off after it had run for an hour 10.2

Hoping for some perspective. I don't know too much about how this all works. Does it seem like I should replace the batteries? How do I rule out an alternator issue? Alternator picture is attached. The battery charger is 10 amp and plugs into AC and then attaches to the battery terminals in a simple way. The alternator connect is a bit less obvious.

 

[Loren Beach]

On the sole question about batteries and possible need to at least consider replacement, what is the date of install on the present bank? Any date stamped or tagged on the battery?

 

[Epenn]

On the sole question about batteries and possible need to at least consider replacement, what is the date of install on the present bank? Any date stamped or tagged on the battery?

2015

 

[bigd14]

A fully charged battery should be around 12.6 volts with no charger or draw. I suspect the battery is toast based on its age, but you could take it to most any auto shop to be tested. I think your alternator output should be around 13.5 or so. Check all wiring and grounds first, then if nothing is amiss it might be worth taking it to an alternator shop for testing.

What is the current battery bank configuration? I recently replaced some 2016 batteries with two 6V Trojan T105 batteries wired in series. That seems to be a common solution for many boats and they fit nicely in the later model 30+ like ours. Also suggest you fuse the positive battery cable when you replace the battery if it's not already done.

Good luck sorting it all out!

 

[Tin Kicker]

My engine will not crank, and other electrical appliances are weak. When I use a car jumper kit, the engine starts up right away as usual. I took the following volt meter readings directly from the battery terminals:

- Battery charger off, engine off ~9.7
- Battery charger on, engine off ~13.5
- battery charger off, engine on ~ 9.7
- battery charger off, engine running for an hour ~9.9
- battery charger off, after engine turned off after it had run for an hour 10.2

Hoping for some perspective. I don't know too much about how this all works. Does it seem like I should replace the batteries? How do I rule out an alternator issue? Alternator picture is attached. The battery charger is 10 amp and plugs into AC and then attaches to the battery terminals in a simple way. The alternator connect is a bit less obvious.

You are missing several things which you ought to try.

First off, clean the electric connections at the alternator, regulator (if external), and battery(ies). A bit of corrosion can keep the alternator from outputting at full current.

Second and what really catches my eye is the charge rate with the engine on because it should be 13.5-ish volts.
An alternator typically needs about 1,500+ rpm before it really starts to give a 13+V charge and the pulleys on most alternators will spin them faster than the engine to get this. But not all will and your alternator may be weak. Since you ran the engine but did not say what the RPM was, I'd suggest checking the voltage with an increased throttle setting to see if the alternator will put out 13.5V.

Then run the battery charger again and see if the battery holds a charge. Or easier is to simply take the battery to the local car parts store and have them load test it because it'd be no surprise if a 7 year old battery needs to be replaced.

 

[G Kiba]

My guess is bad battery. Because you can jump it and it starts and keeps running. Your alternator must be supplying power to your lift pump to keep the engine fueled.

 

[Reefpoints]

If I were you, I would stop trying to diagnose the problem and just replace the batteries. The batteries are very likely dead. Any time a battery is below about 11.6 v, it is being damaged. Please see attached State of Charge diagram

 

[toddster]

I would do as Tin Kicker suggests. All of these symptoms can be caused by a 25 cent connector being loose or corroded.

Start by spending one dollar before spending $800 and then finding that it still doesn't work. (As "professional" mechanics did to one of my vehicles once.)

 

[frick]

My experience is that most marine deep cycle battery are good for 5 years, after that you are on borrowed time.
Rick

 

[goldenstate]

OP says that the voltage readings are taken from the battery terminal (multimeter on the studs presumably) therefore corroded connectors seem unlikely to be explanatory.

 

[Parrothead]

Don't get tunnel vision on just the connections. OP said "Battery charger off, engine on ~ 9.7V" This points to a secondary test at the alternator output post. For reasons as yet unknown, the battery is not getting charged.

 

[Tin Kicker]

OP says that the voltage readings are taken from the battery terminal (multimeter on the studs presumably) therefore corroded connectors seem unlikely to be explanatory.

Au contrare mon ami,

The battery won't charge if there is resistance in the sense wire for the regulator circuit.

 

[goldenstate]

Au contrare mon ami,

The battery won't charge if there is resistance in the sense wire for the regulator circuit.

That makes sense to me in part, but the OP has tried both a charger and an alternator.

My logic is that if the battery reads 13.5 with the charger on, a power source is supplying adequate voltage to the battery, and the battery then reverts to sub operational levels once the charger is off, then we can establish that there is a problem at the battery.

@Epenn One other easy check: You didn't mention the battery type. If these are flooded led acid / wet cell batteries (you can pry a plastic cap off off some holes on the top of the battery) you need to make sure that you have distilled water in the little receptacles. Buy a $2 gallon of distilled water at your local pharmacy. Put some in a more-pourable container (small squirt bottle) and fill up the little plastic pots. Don't overfill because the water mixes with sulfuric acid.

I inherited wet cell batteries that exhibited similar behavior until I refilled the distilled water. That got me another 6-12 months of light use. Ultimately you will probably need to replace the batteries given their age and their substantial level of discharge.

Cleaning the alternator connector wires as Tin Kicker suggests is also an easy/cheap test and I would try that too.

 

[fool]

@Epenn One other easy check: You didn't mention the battery type. If these are flooded led acid / wet cell batteries (you can pry a plastic cap off off some holes on the top of the battery) you need to make sure that you have distilled water in the little receptacles.

Cleaning the alternator connector wires as Tin Kicker suggests is also an easy/cheap test and I would try that too.

Or, as part of regular maintenance on Flooded Lead Acid batteries, you could try getting a measure of specific gravity from the (H2SO4 aqueous sulfuric acid) “water”.

Use care: gloves, eye protection, no smoking or sparking the leads, to get a sample into one of those squeeze bulb thingies your grandfather kept on a garage shelf, AKA hydrometer, readably available for about $10 bucks. A refractometer, under $20 bucks and readily available, is an easier testing method to read by putting a drop of “water” on a slide and looking through a scope.

You’re looking for a specific gravity in the range of 1.27 in all six cells, on a fully charged battery.

If the numbers for all cells aren’t within a point or two get a new battery. The cells have to be ”balanced” for the battery to maintain a charge. If they aren’t the stronger cells will alway be working to get the weaker cell up to speed.

So, IMHO, while you’re cleaning terminals to connect to that new Flooded Lead Acid Battery, add a little regular maintenance to the schedule to keep the new battery healthier for longer.

Also, L/A batteries do not like to be stored in a partial state of charge and will self-discharge at about 25-30% per month. A maintenance (trickle or float) charge is suggested when connected to shore power.

 

[goldenstate]

Or, as part of regular maintenance on Flooded Lead Acid batteries, you could try getting a measure of specific gravity from the (H2SO4 aqueous sulfuric acid) “water”.

Use care: gloves, eye protection, no smoking or sparking the leads, to get a sample into one of those squeeze bulb thingies your grandfather kept on a garage shelf, AKA hydrometer, readably available for about $10 bucks. A refractometer, under $20 bucks and readily available, is an easier testing method to read by putting a drop of “water” on a slide and looking through a scope.

You’re looking for a specific gravity in the range of 1.27 in all six cells, on a fully charged battery.

If the numbers for all cells aren’t within a point or two get a new battery. The cells have to be ”balanced” for the battery to maintain a charge. If they aren’t the stronger cells will alway be working to get the weaker cell up to speed.

So, IMHO, while you’re cleaning terminals to connect to that new Flooded Lead Acid Battery, add a little regular maintenance to the schedule to keep the new battery healthier for longer.

Also, L/A batteries do not like to be stored in a partial state of charge and will self-discharge at about 25-30% per month. A maintenance (trickle or float) charge is suggested when connected to shore power.

Oy vey! What a great pitch for buying sealed, no maintenance batteries!

 

[goldenstate]

If these are flooded led acid / wet cell batteries

That is, "lead" acid batteries forevanssakes. Fast typing.