Is a Johnson AGM starting battery fully charged at 12.68v???

[Naio]

Buying a new chassis battery, it took me forever to find somebody who actually had an AGM one in stock, as opposed to just claiming they did.

Got it yesterday. Johnson Control,
sold under the Duralast platinum label from AutoZone. Dated August of last year.

Not topped off when I got it. I idled the van for a while yesterday, ran out of time. Battery ended at 12.76 but I assumed that that was just because I didn't charge it long enough.

Today, hooked up a smart charger, and it reads as fully charged, although voltmeter said 12.68 before plugging in charger.

Not much luck finding specs online for this particular battery, and guys at AutoZone didn't even know what AGM was, so I can't ask them.

Is it possible that it really is fully charged at 12.68, or have I got a dud battery? It did start the van, although weather is warm.

Don't know what I would do without you guys.

[2oldman]

Naio wrote:
guys at AutoZone didn't even know what AGM was, so I can't ask them.

That's incredible, or maybe just normal for minimum wage auto parts clerks.

[landyacht318]

Only my yacht is landlocked. Its owner frequently dangles lower appendages as shark bait at continent's edge, with yacht usually visible, with battery charging or already full charged and floating.

[MEXICOWANDERER]

I include safety with working on a buss that has 120 vac and a lady that is not as nerdy as I.

For someone not intrinsically as involved as I with equipment I like to play-it-safe and go step-by-step

Landlocked Yacht, I would never write something like that for you 🙂

[landyacht318]

As far as the order of hooking up the Adjustable voltage power supply, I almost always plug my meanwell rsp-500-15 in to 115VAc, adjust the voltage, then connect my Anderson powerpoles completing the DC circuit to the battery. I do not disconnect it from 115Vac, then hook to battery, then back to 115Vac.

I've been doing it this way since October of 2014.

I've also disconnected it from AC while it was still charging or just supporting DC loads, many many times, but generally try not to.

Basically I try to limit the connecting and disconnecting of connectors and turning things on and off.

My 3600 degree potentiometer for voltage adjustment has a turns counter. I could in theory equate a certain voltage with the amount of turns counted, but instead just spin it at will. Only if the battery is well depleted will a 14.7v unloaded setpoint measured at the power supply, drop below 13, and only for 10 seconds or less as the battery sucks up 40 amps, and my DC circuit could certainly have less resistance at 40 amps.

[MEXICOWANDERER]

I agree with Lifeline that a battery that sits for 8 months at moderate temperatures needs to be charged. My Lifelines like 13.03 volts and will stay there several weeks post charging.

If I had AGM in the toad I would set the voltage regulator at 14.40 and there it would reside.

Using a 2 to 4 years warranty is an admission of administrative maintenance failure. Not my bag. Sooooooooooo easy to use the Meanwell once or twice a month.

[landyacht318]

The ineptitude of the general public regarding charging of starting batteries proves that batteries can and usually do 'just fine' with whatever sort of voltages the vehicle allows.

But we here on this forum know that battery performance and longevity can be greatly improved by proper recharging, which means charge to full, promptly after any significant discharge.

While the heat the underhood battery is exposed to is controllable only to a slight degree by the owner, its recharging cam be amended to a much superior status by the use of external charging sources and the simple knowledge that the vehicle simply does not care about battery longevity and the voltages allowed by it are far from ideal.

A newly purchased AGM reading 12.68v has obviously been sitting on the shelf for a while. Top charging it with the adjustable power supply is very wise. One deep cycle, even on a AGM battery designed for starting purposes only, is not going to damage it, provided it is recharged promptly and to full.

I was unable to get my ~1 month old Northstar AGM, when I purchased it, via a shumacher 'smart' charger to read over 12.85v. While I could tell its cranking amps were quite high as it cranked my engine with authority, it was not until i discharged it to ~50% and recharged it at 25+ amps until full, that its blisteringly high pulse cranking amps became obvious, and thereafter it rested fully charged at 13.06v, and startled me every time I twisted the key to start.

This battery is now, right around the 750 Deep cycle mark. It will have been my sole battery since June 2015 for both house loads and engine starting, it will turn 5 years old in November. The voltage it holds under load for AH removed from it, is still impressive. It has lost much of that extreme ability to crank the engine so fast that it is scary, but it still can start my engine easly depleted 65 of its original 90AH rating, and it only drops to 9.73 volts when depleted 65 of its 90 AH under the ~140 amp load of the starter.

Since you have the tools, and ability, and obvious desire to get the best performance and longevity from your new AGM battery, I would say, after following the protocol outlined by mex to top charge it) to discharge the thing to the 50% range and recharge it at 25+ amps until it reaches 14.7v and until amps taper to under 0.4. When you do turn the key to start the engine thereafter you might be shocked at just how fast it cranks and fires up, and its resting full charge voltage will likely be 12.95+ .

Or you can say it will be 'just fine' as is, and it very likely will be.

But working 'just fine' is subjective and in some instances can be little better than 'it will fail tomorrow'.

I'd rather have something work to its maximum potential, as opposed to 'just fine'.

An Adjustable voltage charging source, and an ammeter will allow you to achieve maximum potential, if you choose to do so.

Turning on the headlamps on high beam is likely a 15 amp load. 3 hours of it should take the battery to the 50% range. The goose it to 14,7v with 25+ amps, and hold it there until amps taper to 0.4 or less.

[BFL13]

Naio wrote:
Thank you, both!

And Mex, I honestly appreciate the very detailed instructions :-). Did not realize I should set the voltage when disconnected. It's at 14.72v when disconnected, so I didn't adjust anything, just hooked it back up. It's taking 2 amps still.

With the charger set to 14.7 and if the battery is at 12.4 when connected, the voltage you see will be somewhere between those. So to set the charger's voltage, you have to disconnect the charger to see what its voltage really is, then connect to the battery. (with the 120v not plugged in yet)

The idea to clamp the charger onto the battery first and then plug in the 120 comes from the input hit the charger takes if you clamp on while it is plugged in. Easier on the charger to clamp on first then power it up.

When you are charging and want to set the charger's voltage higher, you can twiddle the dial and see a new voltage, but you don't know what you actually set the charger to. If you dial it down, you get no amps until the battery voltage falls below the new charger's voltage, so it looks for a little while that something is wrong, but it's not.

My deep cycle AGMs have a resting voltage of 13v when full, but I don't know if all AGMs are like that. Also their SOC voltages are higher than Flooded by maybe 0.2 volts, but you don't care about that with a starting battery.

[Naio]

Thank you, both!

And Max, I honestly appreciate the very detailed instructions :-). Did not realize I should set the voltage when disconnected. It's at 14.72v when disconnected, so I didn't adjust anything, just hooked it back up. It's taking 2 amps still.

[landyacht318]

I'd set meanwell to 14.7v until amps accepted are less than 0.4, but I would also prefer to know the size/ ah of the battery before deciding on 0.4 amps but I am assuming a group 24 of less than 85AH capacity

And i would never ever waste fuel idling an engine to recharge a battery, as its voltage regulation is likely only seeking 13.6v, and 1/3 the amps flow at 13.6 vs 14.7.

Idling to top charge a battery is unwise in the extreme, to put it kindly.

AGM restig full charge voltage is usually 12.85+

My Northstar AGM is 13.06v, but I could not get it up there until I did a 50% discharge and recharge at 25+ amps.

[time2roll]

I speculate 2 to 4 year free replacement if it fails to start you vehicle?
I would just use it. Sitting a full year will not hurt much on an AGM.

[MEXICOWANDERER]

• Unplug Meanwell
• Disconnect Meanwell from battery
• Plug Meanwell back in
• Connect hand held meter to Meanwell
• Tweak blue adjustment pot to 14.6 - 14.7 volts
• Unplug Meanwell
• Connect Meanwell to battery
• Plug power cord back in
• Now what do you have for an amperage reading
• Charge with Meanwell until amperage reading drops to ONE-HALF amp or lower
• Your AGM came to you after sitting on a shelf for eight months
• It was nowhere near full
• This is not good for the battery but it can be recovered OK
• It must be charged with the Meanwell at this point, nothing else
• You have the perfect machine to save the new battery
• Please do it

[Naio]

Thanks, time2roll, I figured out I was too low, too. Stupid memory!

What do you think about this battery in general? Should I exchange it?

[time2roll]

I would go 14.4 until you see less than half amp.

I have doubts automotive starting batteries really get to 100% charged. More like 96% to 99% and they do just fine due to limited cycling.

[Naio]

Update: I put my meanwell on it, 1.3 amps at 13.8v, now 2amps at 14.65v.