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Testing Lead Acid Batteries (23 posts / 1,105 views)
Tinhead Tinhead
Posts: 17,089
Post #1 11 Jun 2020 20:23
0
I don't own a bait boat but I'm interested in how people test the condition of lead acid batteries before they charge them.
Do you just wait for them to be obviously flat or do you test the actual voltage of the battery?
If you do the later what do you use and do you know if it puts a small load on the battery. You get a better reading if there's a small load rather than test it open circuit.
carpy09 carpy09
Posts: 14,236
Post #2 11 Jun 2020 20:26
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In reply to Post #1
I put the batteries in the boat have the boat running and plug a digital volt meter display into the bait charging socket and it gives me the voltage . But if I go periods of around 8 weeks and have not used the boat I put the batteries in the boat and run the boat keep stopping and starting it for a hour or 2 then give them a full recharge
Tinhead Tinhead
Posts: 17,089
Post #3 11 Jun 2020 20:53
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In reply to Post #2
So running the boat while it's running
Have you bought a purpose built voltmeter for that job and did it come with instructions to do that.
A what voltage do you decide to recharge the batteries?
Thanks
carpy09 carpy09
Posts: 14,236
Post #4 11 Jun 2020 21:12
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In reply to Post #3
No it's cheap digital volt meter of ebay not sure what voltage they charge at I just use the waverunner mains charger I got with the boat to charge the batteries
Speckledhen
Posts: 133
Post #5 11 Jun 2020 21:20
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In reply to Post #1
I use an Optimate 4 which conditions the battery as well. You can leave the battery on permanent charge with these chargers but I tend to give the battery a charge once a month. I also bring the batteries in from the garage during the colder winter months.
Tinhead Tinhead
Posts: 17,089
Post #6 11 Jun 2020 21:44
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Thanks chaps, I'm more interested in testing the batteries than charging them.

Just read somewhere when reading the battery with a voltmeter...........

Reading above 6.3v or 12.3v indicates battery is fully charged.
Reading below 5.4v or 11.4v battery needs charging.


Just trying to work out whether that sounds right and whether that's tested under load as that's the best way when using a voltmeter.
Old-Cornishman
Posts: 688
Post #7 11 Jun 2020 22:14
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In reply to Post #6
Those readings would be under load.
Fully charged should be 12.7 to 12.85 depending on type.
50% capacity 12.2 to 12.35
Reading taken after battery is allowed to rest for several hours minimum.
Old-Cornishman
Posts: 688
Post #8 11 Jun 2020 22:24
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In reply to Post #5
I don't think you will be doing your battery any favours unless your charger is an intelligent one.
Just using your optimate should be fine.
If you can keep a battery in a good state of charge then it shouldn't freeze in the uk.
Fully discharged and it certainly will.
Tinhead Tinhead
Posts: 17,089
Post #9 11 Jun 2020 22:37
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In reply to Post #7


Any ideas of a suggested load, run the boat or put some sort of high wattage resistor across the terminals?
Old-Cornishman
Posts: 688
Post #10 11 Jun 2020 22:43
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In reply to Post #9
Too many variables to even guess.
Why not test it in its resting condition?
Tinhead Tinhead
Posts: 17,089
Post #11 11 Jun 2020 23:01
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In reply to Post #10
When you say resting is that without a load, I was reading that batteries can give a false high reading without a load and the voltage plummet once it is under load. You need to get rid of the surface charge?
Budice Budice
Posts: 336
Post #12 12 Jun 2020 00:53
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In reply to Post #11
You'll only get surface chrge from a battery that's just come off of a charger. In themotor trade anything below 12.5v needs to be recharged
AJM123 AJM123
Posts: 558
Post #13 12 Jun 2020 06:13
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In reply to Post #1
I don't own a bait boat (yet) so i cannot give you specifics.
But a lot of the new boats i've seen either have a voltmeter on the handset or boat, and/or they use a traffic light type system to show the battery state.
If the boat didn't have any of those then i would just use a multi meter across the terminals as has already been discussed.
Old-Cornishman
Posts: 688
Post #14 12 Jun 2020 07:01
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In reply to Post #11
The surface charge is gone after resting the battery without load for a day.
I've two batteries in my garage, both fully charged. The one on a float charge will be about 13.2 ish and an almost new one sitting on the shelf which will be at 12.7.
As Budice says the surface charge is only present after coming off charge. If you want a quick reading, load it for a short while.
Speckledhen
Posts: 133
Post #15 12 Jun 2020 08:10
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In reply to Post #8
Cheers, i only use the optimate charger. It was recommended to me by bikers. The only reason I bring the batteries in during the cold months is I don't believe it does the batteries any good leaving them in the cold. I could be wrong on that point but it doesn't hurt and my batteries bar one have been going strong since 2007.
Old-Cornishman
Posts: 688
Post #16 12 Jun 2020 08:46
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In reply to Post #15
Without doubt the capacity of a lead acid drops significant when its cold (50% @ -18 deg C) but as far as I know no permanent damage should occur if it's fully charged. As you say bringing it inside during the winter doesn't hurt if you have the space.
However using a lead acid battery at high temperatures will reduce its life so it's advisable not to leave a boat cooking in strong sun before use.
Tinhead Tinhead
Posts: 17,089
Post #17 12 Jun 2020 08:55
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In reply to Post #13
i would just use a multi meter across the terminals as has already been discussed.

That's really the point of creating this thread. Batteries can have a high voltage reading but as soon as they have a load put on them they can plummet.

Most people just probably recharge when the batteries are obviously dead which is fair enough but if you want to measure them then it may not be so straight forward.
Old-Cornishman
Posts: 688
Post #18 12 Jun 2020 13:21
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In reply to Post #17
Testing under load is pretty much meaningless unless you have manufacturers data to go by.
Possibly you could take some readings with a new battery to compare the degradation but resting voltage is the best for us imo.
At home rest for 24 hr off charge, off load and ideally unmoved before taking a reading.
On the bank, if you are charging, take some power say 1 or 2% of the capacity before taking a reading, whether charging or using, its best to rest as long as possible before taking your reading.
Do not let the voltage drop below 12.4 otherwise it will be reducing its life.
Store fully charged, keep as cool as possible in summer otherwise battery life will be reduced, keep charged in winter to prevent freezing



AJM123 AJM123
Posts: 558
Post #19 12 Jun 2020 13:39
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In reply to Post #17
I must admit i am slightly confused as to what your trying to ascertain, and if you are referring to a bait boat with used batteries or brand new batteries?
All batteries degrade over time and with repeated charges.
A leisure battery for example will usually be rated on the number of charges it will take over it's life cycle.
With respect i feel you might be trying to over complicate the issue.
With regards to a bait boat it's probably best to use an LCD voltage display meter which will numerically tell you what the state of the battery is at the time, so you know when it will need recharging.
Over time if you feel that it is not holding a charge and is depleting quicker than usual then if that is not remedied by giving it a good long charge it's time for a replacement battery.
From what i've seen batteries for bait boats are not excessively expensive so it's not something i would personally obsess over.

I hope the above doesn't come across as arsey.
It does sound a bit like it when i've re-read it.
But it's not meant to be.
Tinhead Tinhead
Posts: 17,089
Post #20 12 Jun 2020 14:59
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In reply to Post #19
With respect i feel you might be trying to over complicate the issue. Yes probably.

It was when I noticed voltmeters being sold as battery testers it just bugged me . Yes they may give some sort of indication but it's not technically correct. Just wondered if anyone had better ways of doing it but it probably doesn't really matter that much , just me being anal
Budice Budice
Posts: 336
Post #21 12 Jun 2020 15:46
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In reply to Post #20
If it's a 12V battery you're looking to test them something like this would be fine
Tinhead Tinhead
Posts: 17,089
Post #22 12 Jun 2020 18:55
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Done some googling and this is what I'm trying to get at by testing batteries under load.

LINK 1

LINK 2

LINK 3 scroll down a bit

A multimeter with battery load test function built in

People have their testers or just wait for batteries to run flat and it works for them so there's no need to change but I think I have cured my own curiosity even though I don't own a bait boat

Old-Cornishman
Posts: 688
Post #23 12 Jun 2020 20:08
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In reply to Post #22
I believe I understand what you are getting at now.
Two distinct things being discussed here, hence the confusion.
1. Testing whether the battery is serviceable, normally a high current is drawn (to replicate car starting current for instance) and a certain voltage should be maintained unless there are dead or dying cells.
2. State of charge measurement by a multimeter as discussed previously.
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