Walmart Marine-Maxx Batteries

[Obelix]

This is a question to all the "engineering types" on this forum.
I purchased recently 2 Group 29 Marine-Maxx batteries at Walmart and have serious questions if they accept a full charge.
After discharging the, according to my Prosport intelligent charger, fully charged batteries for 6 hr's at <C/25 I should read >75% charge remaining, but the no load voltage is only indicating about 60% remaining charge. Here is the question:

Does any one of you have a lead-Acid battery typical discharge-chart showing Voltages over time at different discharge rates?

I try to ease the runaround I most likely can expect when trying to get them exchanged.
Thank you for your replies.

Obelix

[seahouse]

The voltage reading during charging is not really significant, the battery needs to have rested to get a more realistic estimate of state of charge by voltage. Of course, the specific gravity measurement is the most meaningful for determining state of charge, not the voltage, which is the average of the 6 cells. Also know that a brand new battery needs to go through several cycles before it's at its maximum performance ("break in"), then it degrades from that point over time.

Let the charger fully charge the battery, let it sit for a bit, then measure the voltage if you want the most reliable figure. Record that as a reference reading for each battery for later.

Chart is in this link- scroll lower on the page.

http://www.solar-electric.com/deep-cycl ... 20Voltages

- Brian.

[Obelix]

Brian,
Thank you for the reply.
Here is my problem, the red line shows what I measured and the blue line shows what should be expected.



Obelix

[seahouse]

I see the discrepancy Obelix, but there are a lot of unknown variables in this situation that can change and move the curve.

How can you be sure that your charger is supplying at C/20 ? - smart chargers supply at a varying rate that might not conform overall to the C/20, or any other fixed-rate curve.

The results you are describing are happening on charging, while the curves on the chart are discharge curves, which are different; that alone might account entirely for the offset. The graph is a bit misleading though, in that the x-axis should be reversed, going from 100% to 0% as t would, so that makes it appear as a charge, instead of discharge, curve would.

The graph illustrates that lower discharge rates give you a higher battery capacity than high discharge rates, but the actual shape and slope of the curve would depend on the individual construction and technology "fingerprint" of any particular battery and charger. I'm not sure that any charge curves you are looking for that you might find would be close enough for the diagnosis you want, though, for the same reason.

If you want peace of mind on these two batteries, the ultimate test of their capacity is to charge them fully (say, overnight, to full voltage), then take them to a well-equiped auto centre and have them do a load test (usually free).

[Obelix]

Brian,

This is not a charging graph but a discharging graph, the voltages show the percentile of charge remaining while using different discharge-currents. The batteries were fully charged overnight and I was discharging at 4.3A (metered) equaling about C/25 for a 114 Ah battery. The discharge took place with a constant load and the ending voltage Is temperature compensated to 68⁰F, using a factor of -0.012V/⁰F.

I had them tested when I purchased them in Oct 2013 at Walmart and the test came out OK, so I was told. Maybe the auto-center idea is not to bad.

Obelix

[andyman2000]

have you used a hydrometer to measure your battery? That will tell you the condition of your battery.

andy

[andyman2000]

Let me just add a couple more things. If you want to know the condition of your battery, go to harbor freight (find a coupon so you can get 20 percent off), buy a load tester for $20 and also buy a hydrometer tester.

you'll want tohe 100 amp battery load tester on sale now for $19.99 .. don't get any of those fancy digital stuff.

Then go to your nearest auto parts store, oreilly, and buy a battery hydrometer. Get the one that looks like a turkey baster with the meter inside the tube. I think its like $6.19

The above will tell you the conditions of your battery and at the very minimum will tell you which battery you have is weaker. No need to bring your battery to an auto center where all they want to do is sell you a new battery.

And if you had to buy a new battery, go to costco. Better return policy. I bought 2 costco marine batteries for my 26M.

Once you have your battery sorted out, get yourself a solar panel charger . Marine batteries do leak charges and self discharge at 1-5 percent . If you don't charge, your almost gauranteed a 2-3 year life span vs something much higher. But to be fair, I have a 2006 costco marine battery in my truck and its still going strong.

[Boblee]

Not an engineer (just a sparky) and not really understanding what you are really trying to relate or at least achieve but have been reliant on batteries for many years when travelling.
As for voltage it is as Brian says the only voltage that counts is after the off charger stabilisation period and even that cannot give you a full story on the health of the battery.
If you want to get your batteries fully charged especially sealed batteries where you can't use a hydrometer the best way is to use an intelligent charger and the best I know of is the c-tek range, when the charger drops back to float or 13.8v the battery is charged, measure from start till that time.
This is not to be confused with up to 14.4v during the charging process or even the 15.2v recond mode as it only allows limited amps.
Your fully charged battery after stabilisation time? should be 12.8v but finding a battery that gives 12.8 is no guarantee that it is fully charged.
You can watch your older el cheapo charger and when it drops back to a very low amperage you could say it is probably charged but you will not know for sure which could shorten it's life.
You can safely say that when any of the modern batteries are down to 11.2v they are flat and need charging as to what level of useful charge is still left in them?
The starting voltage eg eg 11.2 or 12.2 will determine what level of amps the charger will provide but the timeand rate of charge curve is not linear and don't forget you need to allow up to 25% more time to allow for losses.
Good luck btw what type of batteries are they but even knowing that doesn't help as they are all hybrids now.
EDIT Just had a re read of the posts and it appears you are trying to find out how long it will take to charge if they drop down to a certain voltage(%), this cannot be measured exactly as the rate of discharge is not linear as the amps change with the voltage for a given load when discharging and conversly the charger rate changes as it charges.
To further confuse your voltage would need to be taken prefferably under full load as if load is disconnected the voltage will rise substantially for quite a period after removing just like it will drop after removing the charger.
Tip get a good intelligent charger, don't let voltage drop below 11.2v (small load) and charge till float level, batteries will last ten times longer otherwise get a small regulated solar panel to leave on trickle.

[DaveB]

I am on my second set of same batteries you are using. I have a 10 amp built in battery charger that charges two banks. One bank is twin group 29 and other is group 24 for engine starting. Charger charges both groups separate on 110 volts. I have a Diode that prevents discharge from one bank to another when on 12 volt.
I have a 2 types digital volt meters pluged into Gig. lighter that shows my voltage.
I run 63 quart edgestar frig. and the twin house group run off that.
I have no charts but have taken info times in how much it takes to down the house to 12.2 volts. 50% discharge.
I run my frig. on a 100 watt inverter as my 12 volt cable failed and using the inverter requires lot more juice.
Need to hot wire the DC cable to the House battery bank.
That will happen when I retire jan.31st.
Hope this helps out but remember when on my back yard I have a 110 outlet that auto charge my batteries.
I also have twin 40 watt solar panels with a 6 amp controller and those who don't have 110 can easy use a Solar panel of 40 watts and also a controller of 4amps or more.Thats so you always have fully charge batteries and they don't sulfate.
Dave

This is a question to all the "engineering types" on this forum.
I purchased recently 2 Group 29 Marine-Maxx batteries at Walmart and have serious questions if they accept a full charge.
After discharging the, according to my Prosport intelligent charger, fully charged batteries for 6 hr's at <C/25 I should read >75% charge remaining, but the no load voltage is only indicating about 60% remaining charge. Here is the question:

Does any one of you have a lead-Acid battery typical discharge-chart showing Voltages over time at different discharge rates?

I try to ease the runaround I most likely can expect when trying to get them exchanged.
Thank you for your replies.

Obelix

[raycarlson]

Not sure that you understand what really matters, don't waste your time trying to chart discharge rates.Worry about a full charge as a #1 priority i.e at least 12.8V after a 24hr resting period from coming off charger. If your batteries accept a full charge and pass a load test Walmart will NOT exchange for warranty nor anyother store would either. If your convinced you got a bad battery(which you probably don't) just pop off the cell cover and take a long screwdriver and hammer and perforate your plates inside,then replace covers and take into walmart, then they wont pass any kind of test and they will replace one, I wouldn't do both as that's highly suspicious.

[Obelix]

raycarlson,

Not sure that you understand what really matters

Thank you for setting me strait, but following your approach will not clarify what the real capacity (Ah) of these batteries is.

Obelix

[sirlandsalot]

Walmart is the enemy, the demise of our society. It is Karma because you shopped there.

[topcat0399]

Walmart is the enemy, the demise of our society. It is Karma because you shopped there.

+1

[Boblee]

raycarlson,

Not sure that you understand what really matters

Thank you for setting me strait, but following your approach will not clarify what the real capacity (Ah) of these batteries is.

Obelix

Easy forget about quoted figures look at practical operation ie
FULLY charge the battery/s put a designated load on it until it drops to your bottom limit remembering that it will bounce up a little after removal of load that IS your useful ah's or amps x hrs, if you are really desperate to know what your useful AH's are at certain stages compared to volts take readings, all batteries will be different as will these batteries as they deteriorate.
Remember when recharging you will need to replace up to 25% more amps than what you took out, unfortunately unless you use a very small charger you will not be able to measure this but it is irrelevent.
To know how long it takes to recharge your battery/s use your designated charger and measure time from when you discharged to your low point until the battery is again fully charged and if keen keep voltages and times during the process.
Anything other than what it means in the practical terms above is irrelevent as there are too many variables and even the practical results above will vary over time etc.
As Raycarson said the most important thing is to fully charge your batteries, have seen too many people stating that their battery is no good but the real reason it wont "hold" charge is because it was never fully charged or and just as importantly the load they want to run is suffering from voltage drop due to too small leads or being too far away, measure voltage at battery and load terminals under load conditions, .5 of a volt drop means 30%+ of your useful storage is locked in your battery if you have 11.2 voltage protection on a fridge etc or if cut off load voltage is measured at load.

[Obelix]

Boblee,

My problem is the possible discrepancy between the quoted Ah's and the amount I seem to be able to extract from these batteries. To make this better understandable here is the charge/discharge data for one of the batteries:

You may note, that the battery is fully charged after a >24hr charge and the charger supplying 13.3V float voltage.
The first partial discharge after drawing <C/25 for 6hr's should result in a remaining capacity of >75% at voltage under this load of about 12.5V (see discharge graph above). In reality, the ending voltage was only 12.06V, representing a remaining charge of about 27%. The no-load voltage then recovered to 12.31V by the next morning. When I started a second like discharge-cycle in the afternoon, the no-load voltage had slightly dropped to 12.3V and under <C/25 to 12.17V when the discharge started and dropped to 12.05V within the next 15 min. At the end of this discharge-cycle the voltage was 11.78V, representing a remaining charge of about 18%. It seems, I used about 46% of the batteries capacity, but I depleted >80% according to the discharge voltages.

Obelix