How to truly determine start battery condition. False sense of security

[Simi 60]

Originally Posted by BlackHeron

.

Your symptoms sound a little bit to me like a bad engine ground. Also, you can have your alternator checked for bad diodes. Bad diodes be will give poor charging (or no charging) and in some cases actually discharge the battery slowly.

I have been chasing issues by elimination on this genset for a while.
All bolt on connections have been removed, cleaned and redone.
Dodgy wiring harness joiners have been cut and redone.
Permanent magnet alternator has been swapped for new spare.

As I said earlier, connecting it up to one of the primary engine starts gets instant results leading me to believe it is a genset start battery issue simply not holding enough charge to activate the solenoid.

[Cpt Mark]

Originally Posted by Scott Berg

We use both conductance testers by Midtronics and a Snap On carbon pile load tester. At a cost of over $800 each I don't expect a cruiser to have them in their kit, but every decent electrician will have similar tools and can do the test for either free (hoping to sell a battery) or very little. It takes me less than 15 minutes to test a two battery bank and that includes disconnecting and reconnecting the batteries.

As noted, a fully charged 12v FLA or AGM battery should show a no load resting voltage of about 12.7v

As an aside I replace our starting bank every 4 years just because (we get 7-8 out of our house bank).

Disclosure: I do this for a living but am not asking to do yours...

An easy and cheap way to check your battery is to put a multimeter on it and get a reading. Then have someone turn the key and not start the motor but just use the starter for 10 or 15 seconds. While they are doing this, use the multimeter and read the voltage. Anything below 10.5V it's time for a new battery

[Taipe]

The gold standard is to measure the current (i.e. amps) under load. The simplest way for most of us, is to take the battery to an autoparts store that can put a load on it. They do it for free and will probably have a 4 point read-out scale (e.g. poor-fair-good-excellent) for you to see when they do it.


Electronics marketing ads claim that their digital solid state voltage meters will correlate with the health of a battery, but none of them can do any better than a rough estimate unless they include current flow data in the analysis. It's obvious that if a battery never gets beyond 12.2 volts after 24 hours of bulk & equalizing charge on a quality charger, you should replace it. But, if it reads 12.6, by voltage alone, it's anybody's guess as to how much life it has left in it, unless they know the history of the battery (i.e. how many times it has suffered a sustained discharge well below 50% of the fully charged cold cranking amps when new).



For general battery maintenance contact the battery mfg for tech support. They ought to be able to share the graph for your particular battery, the specific density relative to percent of maximum charge. Spec. gravity hygrometers are available in most auto parts stores. The float tube type are more accurate than the levered dial type. Every battery bank should have this hygrometer readily available.



Btw, when you buy a new battery, don't take the store clerk's word for it that it's fully charged. At best, all they know is how long it's been since the ones on the back row were charged. Before I put a battery into service, unless I am pressed for time, I do myself the favor of fully charging it myself.

[senormechanico]

HyGrometer:



A hygrometer (/haɪˈɡrɒmɪtər/) is an instrument used to measure the amount of humidity and water vapor in the atmosphere, in soil, or in confined spaces.


HyDrometer:


A hydrometer is an instrument used for measuring the relative density of liquids based on the concept of buoyancy. They are typically calibrated and graduated with one or more scales such as specific gravity.



From Wikipedia, the free encyclopedia
Not to be confused with Hygrometer.

[RaymondR]

Give the engine a good long crank with the engine kill pulled out and see how it handles it. If the battery is doggy it will usually crank down fairly quickly.

[Simi 60]

Originally Posted by RaymondR

Give the engine a good long crank with the engine kill pulled out and see how it handles it. If the battery is doggy it will usually crank down fairly quickly.

Not the best idea.

. Hydrolock Help. The most common cause of hydrolock on a marine engine is cranking the engine over with the starter when the engine is not firing. As the engine cranks over, the water pump">raw water pump is pushing water through the heat exchanger and into the exhaust/muffler.
https://www.sailmagazine.com/diy/hydrolock-headache

[hellosailor]

"The simplest way for most of us, is to take the battery to an autoparts store that can put a load on it. "
Yeah, simplest.
If it doesn't cost you $100 to replace the jacket or pants you splashed acid on. Or the car's rear carpet ($500) or trunk liner ($350) because some acid snuck around. And assuming the minimum wage guy in the auto parts store (the older wiser ones don't play with acid) knows how to use the gear, not all do. And some misuse it on purpose, to sell more batteries.
And no matter how you spell "turkey baster" those outstanding devices spatter acid around. And, you can't check the electrolyte until the battery has stood unused for 24 hours to allow that to circulate and equalize--same reason you're waiting before using a multimeter.

If I'm gonna drag batteries around, I'll go to a battery distributor, where all of the baove still applies but they tend to have better equipment and they'll often put your battery on a tester over the weekend and let if actually CYCLE.

Dunno, but I've found the simple multimeter, used on a battery that has been allowed to rest (knocking off the float charge) is a damn good way to tell not the specific state of charge, but rather, if it is REALLY in need of replacement, or still good to go. Whether it is off by five or even 15% of the real SOC? Not critical. You're in the ballpark, with no acid, no hefting heavy loads, no fuss about it.

Assuming of course, you've got a calibrated or known good meter, not just the $5 junk from Horror Fright. Which sometimes is dead on, other times off by 0.4 volts, right out of the box.

[Bycrick]

The battery in question is a starter battery. It’s rated in Cranking Amps, ie the number of amps that the battery can supply for 30 seconds without the terminal voltage dropping below 7.2 volts. A good group 31 battery will be 600-800 cranking amps. So, if you measure across the battery terminals while running the starter motor for 5-10 seconds, the battery should stay above about 11 volts. If it doesn’t, then the battery is lacking in capacity.

The resting battery voltage, with no load or charging, after a few hours is a good indicator of the “state of charge.” But this number has nothing to do with the capacity of the battery to drive a load. A D-sized (flashlight-sized) lead acid battery will show the same “fully-charged” voltage as an 8-D sized battery cell.

The comment on meter accuracy is right on the money. You need an accuracy of more than 1% to get meaning from a single voltage reading. Most inexpensive DVMs are rated at percent-of-full-scale with the internal circuits scaled to 20 volts. So, a 1% accurate meter will read +/- 0.2 volts of the correct reading. That’s not very useful for battery charge state.

But if the battery is at 12.5 volts at rest and it drops to 11 volts when you crank the motor for a few seconds, you know the battery is weak. That works even with a cheap, inaccurate meter.

[Taipe]

[QUOTE=senormechanico;2828186]HyGrometer:


Yes, I know the difference. But thanks for the spell check.




A hygrometer (/haɪˈɡrɒmɪtər/) is an instrument .....

A hydrometer is an instrument used for measuring the relative density of liquids based on the concept of buoyancy. They are typically calibrated

[RaymondR]

Originally Posted by Simi 60

Not the best idea.

You need to modify the exhaust system if you can't crank for 20 seconds without back flooding your engine.

[BlackHeron]

Originally Posted by RaymondR

You need to modify the exhaust system if you can't crank for 20 seconds without back flooding your engine.

Exactly.

Plus there is the fact that a diesel engine is an air pump, whether it is running or just cranking over. It is still pushing a lot of air out the exhaust, albeit cooler, non-combusted air with unburned fuel vapors.

It takes a lot of cranking to fill the system to the danger point with seawater. If in doubt, you can always turn off the raw water seacock. Just like you aren't going to fill the exhaust with water with 30 seconds of cranking, you aren't going to destroy the impeller in a minute or two of it either. At cranking speeds the RPM of the raw water pump isn't moving all that much water.

[Simi 60]

Well, had my $24 battery load tester , same as HF model shown earlier, turn up at the post office today and the battery checked out fine or at least inside the green is good zone of this hi tech bit of kit.

Back to the wiring betting there must be an extra bad connector amongst the myriad of dodgy connectors that wiring harnesses seem to have.

At least I didn't shell out for a battery that didn't fix the problem.

[RaymondR]

I had a brand new battery which would not crank my engine. On inspection I found that it has an SS stud and two SS washers supplied with the battery. Threw away the SS washers and replaced the top one with a brass washer and let the terminal bear against the lead around the stud and problem solved. At the high currents required to crank a diesel the washers and stud were acting as a high resistance in the current path with consequent extreme voltage drop across them.

[Shaneesprit]

Hi
Crank battery tests - for me its better done old school using this
https://www.amazon.co.uk/Sealey-BT91.../dp/B000R9ZPJK

not promoting the brand or Amazon its just the first link i found.

The point is to understand the test ( and the safety )

Safety first batteries produce gas that can explode, also a dry battery can do the same and in a maintenance free battery the same applies and you cant check the fluid levels - having said that i have never seen one fail on test, but i have seen the remains of ones that went bang from being on charge or under starter loads.

Obviously test batteries when disconnected
The test, if you do it yourself the first thing is you have to be positive with the connection it will spark a bit but the firmer you are the less that happens.

Test for around 10 seconds
normal you will see a drop to around 9 Volts more or less straight away,
if the Voltage drops below this even at 9 seconds into the test then the battery will soon fail.

The problem with the above test is the high load on the battery so possible safety issues, also i have taken my battery's to the Auto battery suppliers and they are mostly untrained and I watch them test the battery for 3 seconds and tell me its fine, then have to explain the test to them, also i have had them use the tester properly and then tell me it failed when it was OK!

There are modern battery testers and most manufactures insist you you a modern tester if you were trying to claim warranty, and in any event the test stops the testing person from badly diagnosing.

Someone said you cant test the house bank! of course you can and its easier disconnect all of the chargers, load up the AC ( Fan heaters are always a good source of load ) calculating the AC loads you are using side while measuring the AC and DC Voltage, and run the test for the time you expect the batteries to last, or until the voltage drops.
This is industry standard and there are lots of companies that specialise in this.

but i believe the point of this is that you have problems with your generator?
make? Model? history of what you have tried already? maybe i can assist you with information on best course of action?

[wingssail]

Originally Posted by Simi 60

Just wondering how to truly determine start battery condition.

Our starts (2x 1000cca 12v @ 24v) are only for the engine and anchor windlass and have never given any hint of trouble in the 2.5 years we have had the boat but, about 18 mths ago I decided to run the "trickle charger" wire from our victron inverter/charger to these batteries so they are always 100% good to go...........or are they?

Is that trickle charger giving us a false sense of security?

The reason I ask this is our 12v genset battery has the little window with green circle and red centre indicating battery is OK.
Voltage indicator reads 12.6 and as low as 12.4 after sitting for several days yet when I put a battery condition tester on it (do they even work?) on it reads as battery OK but low charge.
Pre heating glow plug saps power out so not enough grunt to pull the fuel solenoid in yet there is still plenty of grunt for cranking.
A few minutes on a 4amp battery charger and all is good again quick easy start and voltage reads 13+v shortly after.
I could put a trickle charger on the genset battery as well and for less money and drama than getting a new battery and all we appear to be good but is that really the solution?

So, back to the title of the post "How to truly determine start battery condition?"

Of course a load test with a high end load tester conducted by a professional will be the best, but If you want to know if your starting battery will start your engine, do this:

After fully charging the battery switch it off and make sure no loads or charging current is present.
Leave it for at least 24 hours, (48 is better).
Switch it on and go through the whole start sequence, but crank it with the kill switch engaged (10 seconds, no more).
If your engine cranks fast for 10 seconds the battery will probably be able to start the engine.
Go ahead then and start it (to clear the fuel and water).

If it does not pass that test then it needs replacing, however, if you can perform a equalization, that might recover it. Worth a try.