12v battery drops to 11.5v in 1 hour - Normal?

[BaitThrower]

Hi guys... Just wondering if a battery I have is a dud or not. Bought new about 5 months ago. Only had about 5 charge cycles... 12v 18A/h AGM battery.

Anyway I charge it up using 3-stage charger... After it cools down it reads 12.7 - 12.8v on the digital multimeter, whiwould seem to indicate a full charge.

When I am out boating and have the sounder on, which has a battery readout, the battery reads about 12.6v when I first start, then within about an hour or so it drops below 12v, then drops further to 11.5v... Is this normal? This is with a 27mhz radio operational too. Basically I can see the voltage dropping by .1 each 10 mins or so... 12.6, 12.5, 12.4, 12.3...... 11.5....

Is it normal to drop to under 12v when under load? I havent really run anything for more than say 2 hours continuously, so wondering whether it will just sit at 11.5v for the next 12 hours or so of battery life it **should have** considering the load I have on it. ??

[wiz]

What you really need to know is how much current you are drawing

if your setup has a high resistance it will draw excessive current

check the draw of the two units and then check the specs

cheers

[skipalong]

a battery will always drop under load, depending on how old the electronics you are using and the amount you are running, when you are driving the boat i would say that you shoulkd be getting a charge of 13.8v or more and at rest the battery should read 12.6 or more, but if you think that the battery is suspect at all get someone to put it on a load tester accross each cell,

[Simmo2]

What you really need to know is how much current you are drawing

if your setup has a high resistance it will draw excessive current

check the draw of the two units and then check the specs

cheers

LOW Resistance... Other than that your post is quite correct, and good advice.

[groverwa]

BaitThrower

What is the load in amps?

How does the manafacturer rate the battery over how many hours - I know you said 18A/h but my recollection of Telstra batteries of 3200 A/h meant that you could drag 320 Amps for 10 hours for a battery in good condition

So if 18A/h is for a 10 hour rate then you can drag 1.8 amps and for a 20 hour rate then you can drag 0.9 amps and the voltage will drop over time

Mike

[wiz]

I = V/R you are correct




It is a AGM I doubt it is connected to the motor

[BaitThrower]

Well I've got a Garmin 300C colour sounder. I dont know how much this draws as it is not mentioned in the manual, but I think the battery was doing the same with a Garmin FF140 sounder which was rated as 0.5a/h. Then just the GME GX300 radio, whatever that draws? All electronics virtually brand new. It is a sealed battery so don't think you can test each cell?

13.8v when driving boat? Why would it be that high? My motor doesnt connect to battery to charge it as it goes... only 15hp. Is it normally 13.8v when a motor is charging it?

Umm the 18A/h rating... i dont know how they rate this, but even if its way overated, it sounds like it should still deliver well over 12v at least for an hour yes? The voltage is bleeding away right before my eyes :(

FWIW, its an AmpTech AGM I bought from BIAS.

[BaitThrower]

What you really need to know is how much current you are drawing

if your setup has a high resistance it will draw excessive current

check the draw of the two units and then check the specs

cheers

How do you do this? I have a digital multimeter but so far I only know how to check battery charge with it. Can you also use this to test draw? I suspect it is one of those other settings on the multimeter dial but not sure which one, and what procedure is required etc. Help appreciated :)

[wiz]

you will need to set the multimeter to read amps and take the pos wire off batt and connect one of the test probes of multimeter to the pos wire and the other test probe connect to pos on batt. ie make the multi meter complete the circuit between pos wire and pos terminal of bat

[BaitThrower]

you will need to set the multimeter to read amps and take the pos wire off batt and connect one of the test probes of multimeter to the pos wire and the other test probe connect to pos on batt. ie make the multi meter complete the circuit between pos wire and pos terminal of bat

Ok cheers mate will try that. I guess the negative wires should stay connected on each device? Actually, stupid question, I guess they are needed to make it run :)

[wiz]

yes leave neg wire as is

[BaitThrower]

yes leave neg wire as is
Cheers mate. Appreciate your help. Will tdo the tests and report back with findings.

[groverwa]

Your battery starts at 12.6v and drops slowly over time - normal

So without knowing the load current and the specs of the battery I now think that there is no problem as it is normal for the battery terminal voltage to drop slowly after an initial quick drop - see attached pic of a discharge curve from http://www.users.bigpond.com/solarbbq/batteriesrejuvenating.htm for a deep cycle battery and the current drops a bit also in this case

Please PM me with the type and manafacturer of your battery and I will try to get the specs of the internet

So as I said before we need to know the load current and specs of the battery

As was stated you can take the battery to a dealer and get them to do a test on it for your peace of mind

BTW - current flowing through a circuit equals the voltage divided by the resistance of that circuit - Amps = voltage/ resistance so a low resistance will cause a higher current drain from the battery

Mike

[BaitThrower]

Ok here's the results of the current draw tests:

Note that this is with the setting on the multimeter at "10A" setting.
Note I used the same procedure as outlined in this video:
http://youtube.com/watch?v=yrpmq2FCnqs&feature=related

Sounder: About - 0.27 average
Radio: When sitting on a channel - 0.12
LED Nav Lights: 0.11
LED Cabin type light: 0.13

So I guess the total for radio and sounder on at same time would be about 0.40 average...

Now, what does this reading actually mean? 400ma or 4A ???

Battery is an "AmpTech" 12v 18Ah sealed AGM purchased from BIAS boating.

[groverwa]

Dean

That would mean the current drain is 400mA or 0.4A and this agrees with the info for the sounder I found on the net

We still need the specs for your battery to see what we should get or you take the battery for testing

Mike

[BaitThrower]

Dean

That would mean the current drain is 400mA or 0.4A and this agrees with the info for the sounder I found on the net

We still need the specs for your battery to see what we should get or you take the battery for testing

Mike

Battery is 12v 18 Amp Hour "AmpTech" AGM battery. I don't have any other specs on it and can't find a manufacturers website. I suspect its a rebadged OEm battery from somewhere in China. Apparently these batteries are supposedly quite good though.

Ok so my current draw is 400mA average with both sounder and radio on... so assuming my battery is giving 18 hours of use at 1 Amp each hour, all this gear should run for at least 36 hours! Not 1 hour!
:)

[ronmac]

www.agmbatteries.com.au (http://www.agmbatteries.com.au), their based in QLD. cheers ron.

[ronmac]

sorry all, wrong email address on last post. should have been, www.absorbedpower.com/ (http://www.absorbedpower.com/) my apologies, cheers ron.

[BaitThrower]

Ok found some info on the battery sticker itself:

Cycle Use: 14.4v - 15v
Standby Use: 13.5v - 13.8v
Initial Current: Less than 5.40A

Now I'm not 100% sure what these figures mean, but it sounds like this battery should be reaching a charge up to 14.4v - 15v after charging?? Do I have that right?

Also, yes this is pretty similar to the battery I have:
http://www.absorbedpower.com/battery/pdf/GT12-18C.pdf

According to that, even if I start at 12.7v, I should get at least 10 hours use at 1.0A current draw... Something isnt adding up, and the battery seems to be the common denominator.

[BaitThrower]

Ok found some info on the battery sticker itself:

Cycle Use: 14.4v - 15v
Standby Use: 13.5v - 13.8v
Initial Current: Less than 5.40A

Now I'm not 100% sure what these figures mean, but it sounds like this battery should be reaching a charge up to 14.4v - 15v after charging?? Do I have that right?

Also, yes this is pretty similar to the battery I have:
http://www.absorbedpower.com/battery/pdf/GT12-18C.pdf

According to that, even if I start at 12.7v, I should get at least 10 hours use at 1.0A current draw... Something isnt adding up, and the battery seems to be the common denominator.

Any comments on above guys?
I've got the battery back on the charger and its showing its in trickle mode now after charging up so will leave it on until I head out tomorrow. If it eats up the battery juice at a ridiculous rate again, I'm going to take it back to the shop for replacement. You never know. It could have been sitting on the shelf for many months and discharged itself to damage level...

[Gilli]

hey mate,

To me that sounds like your battery is stuffed, have u tested it with a hydrometer?

if so, and all is good, connect your ammeter up to it and turn one item on at a time, work out which one is drawing how much current then turn all on at once and find your total, you should be able to narrow it down to one item playing up

Then if all that passes check all cable insulation, could have breakdown somewhere along the circuit, get an insulation resistance/continuity tester*also known as a megger) and test all the lines.

regards,
Chris

[QF3 MROCP]

BaitThrower,,, have a read of pages 28 onwards, it'll give an idea about load test and specific gravity testing of your battery...

http://www.amcom.amc.edu.au/handbook/amc.omc.mrohb.08.pdf

[BaitThrower]

Thanks guys. I cant do any specific gravity checking with a hydrometer because it is a smaller sealed battery :(

Anyway thanks for the document. I'll read through it later, but for now, I'm off boating for some more on-water testing :)

[age]

BaitThrower

Couple ofther things I would look at. Check that your 3 stage charger has a setting for AGM type batteries (the CTEK ones do) as your spec indicate that they require 14+ volts to charge up properly. Your charger may be only putting out 12.6 v and you will never charge that battery properly and continually not charging an AGM fully and taking it below 11v will kill it quickly. Run your multi meter across the charger loaded and no load and see what voltage you are getting - to charge this battery it needs to be above 14v. Put the battery on another charger and see if it lasts longer.

Cheers

A

[BaitThrower]

Ok guys... solved the problem.

Basically, it seems like this crappy little three stage charger is telling me fibs. Saying its on float charge even when battery is not charged up to float charge level... Or maybe just me not knowing any different. What I was doing was charging up for say 6 hours, the green light would come on supposedly indicating full charge and charging going into maintenance mode, but this is obviously not the case. This time I left it on for 24 hours and checked it regularly while charging with the multimeter. It was reading about 13.8v average during this charging period. Anyway took it out today with pretty much only the sounder going, and it started at 12.8v, and pretty much stayed there, only dropping to 12.7 volts after an hour or so...

so looks like it just wasn't being fully charged, even though battery charger said it was. Maybe the charger just detects it is a 12.7r whatever and thinks the battery is fully charged... I should just get a better charger probably :)

Since the boat is stored outside, and its a bit of a pain to take the battery out and re-connect it each time, I havent been leaving the battery plugged into the charger for maintenance charge all the time when not in use.

Anyway lesson learnt, and thanks for all your help. I have learnt a few things along the way and hopefully someone else might be able to solve a similar problem if they read through this thread :)

[philpy]

those two things would not come close to drawing 18 amps.Buy a new one mate its not normal

[BaitThrower]

those two things would not come close to drawing 18 amps.Buy a new one mate its not normal

Yep, but see above. Problem seems to be solved.