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MightyMax 18Ah AGM battery
While I can fit 3 group 27 batteries in my van, since June of 2015 I have been using just one single group 27 Northstar AGM battery for both engine starting and house battery duty. It is rated at 90Ah capacity and 930CCA.
     This battery turned 5 years old in late November, and now has over 1000 deep cycles on it to the 50 to 60% state of charge  range, perhaps 150 of those thousand to as low as 30% state of charge.  Even when brought this low it has had zero issues starting my v8 engine in mild temperatures. 

I really do not expect it to live for too much longer, but have been impressed with it to this point.  I am not going to replace it before it fails, nor start babying it, but since it is my only battery, and it is also my engine starting battery, I need to have a backup plan. So I bought this 18 Ah AGm battery linked below for 37$:

This particular '600 watt" model is marketed for the Audio/ Stereo crew but the 18Ah MightyMax battery is basically the same price and weight, 11.9 lbs.

If one plugs in '18Ah AGM' battery into amazon search there will be hundreds of hits, and the batteries themselves might be exactly the same inside, or might not be.  There are some differences in the output terminal design.

I bought this particular model as I like the recessed terminals, that are much less likely to be shorted with a dropped wrench, and I am not really planning on deep cycling it, intending to use it more as a portable 12v source and the occassional jumpstarter battery.  Will this battery be able to provide more CCA, and recharge safely at higher rates than the others?  Well, its marketing might indicate that it was designed for this, but I am skeptical to say the least.   If it were more expensive than the others I would not have bothered getting it over the other batteries in the sub 40$ range.

The UB12180 might be the base battery and all these other 18Ah agm batteries might be the same exact thing internally, or not, the only visible external differences being the terminal design.  Some of them do list slightly different weights, but I do not really trust this figure.  The heaviest one I found was 12.1 lbs, though the UB12180 linked below states  11.4 lbs.

These 18Ah AGMs are used in many of the lead acid jumper packs.  Back in the early 00's before I had dual batteries i had a smaller jumper pack that employed a 12Ah AGM and it was effective in assisting my group 27 starter batttery when i drew it down too low.

Anyway, it arrived today, and read 12.87v out of the box.  I peeled back the sticker but did not see the UB12180 printed below it.

I hooked it up to my 40 amp adjustable voltage power supply and 15 amps instantly took it to 14.7v and began tapering quickly from there.  90 minutes or so later it is still accepting 0.75 amps at 14.7v, so it was not top charged and could have been sitting waiting to be sold for quite a long time, self discharging.  or it might not have left the factory full charged, and most likely some combination of both.

A Brand new battery seems to behave a bit differently than one with a cycle or two on it.  
I am starting this thread to document the lifespan and capabilities of this battery,  using this thread as data storage for future reference.

I intend to see if this battery alone can start my engine, and perform various other experiments on it through its life.

I am not really sure where I am going to store it.  I could put in in my engine compartement, which currently has no battery no battery tray.
[-] The following 5 users say Thank You to sternwake for this post:
  • Wayne49 (01-07-2019), GypsyDogs (01-08-2019), Matlock (01-08-2019), Texjbird (01-08-2019), TWIH (01-13-2019)
Interesting..... Cool
Stay Tuned

Weirdo Overlord  YARC 
15 "Stinkin'Badges"  a "Full Monty Badge" 2 "Just Ignore Me" clusters  4 "Pine Cone" clusters  one "Stinkin' Badger" and 7 of the coveted "Flying Manure Spreader"awards
1 of which is a limited edition Turkey Poop Spreader (What a "Stinkin' " honor !)

As I reported, new batteries tend to act a bit strange before their first cycle.  

The amperage of this new 18Ah AGM tapered to the 0.65 amp level at 14.7v  slowly over 4+ hours, and the battery decided to climb in temperature 0.2 degrees F in a climate controled environment.

I decided to remove the charger rather than leave it connected until amps taper to 0.5% of capacity which would be 0.06 amps.  I dount it would actually taper to tht level, given previous experience with spanking new AGMS.

With a spanking new lifeline GPL-31xt battery, which would be full when amps taper to 0.625 AH at 14.4v, I noticed it refused to taper to less than 0.93 on that initial charging.  One deep cycle to ~50% and 40 amp recharge and the amps tapered as exepected in a normal time frame of under 6 hours.

My Northstar AGm when new would NOT hold a resting full charge voltage of over 13v as Northstar dictated it would, until i did a deep cycle, and 25 amp recharge to full, after which it was full charged resting at 13.06v.

So now I need to actually cycle this new battery once.  Ideally I would try and pull 9Ah from it at a 0.9 amp rate over 10 hours and see where voltage rebounded to in X amount of time, then perform this same test at a later date for comparison.
[-] The following 3 users say Thank You to sternwake for this post:
  • rvpopeye (01-08-2019), Texjbird (01-08-2019), TWIH (01-13-2019)
Ok I busted out a 92 mm 3 amp fan that I can dial in 0.9 amps, except it it too much wind and noise at that amp draw, and my DC clampmeter and wattmeter are not really agreeing with each other even accounting for the draw of the wattmeter itself. The clampmeter is reading about 0.15 amps higher.

Right now the battery is powering this laptop whose battery is full. Wattage is jumping around rapidly from 20 to 33 watts with the occassional 60 watt spike. voltage with a claimed 0.528Ah removed is 12.73 to 12.76.

Voltage had dropped to 13.23v when I started discharging, about 30 minutes off the charger.

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  • rvpopeye (01-08-2019)
I pulled the plug on the load test of this battery.

It powered my laptop through the PWR+ DC to Dc converter for ~4.5 hours consuming 11.722 amp hours for an average load of 2.604 amps.

The voltage fell to as low as 11.61 volts under load, at the end of the test
The maximum load recorded was 5.89 amps, or 70.2 watts
Watt hours consumed --142.5

Once I separated the anderson powerpole feeding my PWR+ DC to DC laptop power supply, voltage instantly rebounded to 11.96volts.

10 minutes later voltage has rebounded to 12.13v, still under the slight load of the wattmeter itself.

2.6 amps of load is nearly 3 times as much load as which the battery earned its 18 amp hour rating(0.9 amps)

Once 11.9v was reached, it seemed to lose voltage much faster than above this level.
I suspect it the voltage would continue to degrade faster and faster from the point I disconnected had I continued.
I also suspect 100% discharged would not be a rested 10.5v, like most batteries, but perhaps closer to 11.0v.

I would need to continue to watch it and see where voltage simply plummetted to the point the PWR+ car adapter could no longer power my laptop, but I'd rather not discharge the battery this low, especially not on the initial cycle.

My conclusion is that the battery performed well, especially considering the rather large load that was placed upon it. Voltage retention was impressive, as i have noticed with Many AGM batteries.
-- One cannot use the regular flooded battery '12.2v rested voltage' for estimating 50% state of charge. I suspect 50% is closer to 12.4v rested with this battery.

Now I will recharge it, letting my 40 amp power supply set loose on it set to 14.7v before hooking up the battery. The UB12180 states no more than 5.3 amps.

I'll see how long it accepts 40 amps before reaching 14.7 volts.
I'll try and see just how long it takes for amps to taper to 0.09amps at 14.7v which should indicate it is fully charged.
I'll use the same wattmeter inline, and see how many AH the battery has accepted

Once below 0.6 amps this ammeter starts readibg progressively lower than actual.
While 11.722 amps seems to be quite exact, i will give that figure an estimation of being no more than 90% accurate.
[-] The following 2 users say Thank You to sternwake for this post:
  • rvpopeye (01-08-2019), TWIH (01-13-2019)

Above it a link to the exact brand of wattmeters I am using to measure current to and from the battery. I have modified mine with 8awg leads replacing the 12awg leads they came with. There are dozens of clones of this wattmeter available all over the web. I have experience with a few of them.

I am using both these wattmeters inline while charging the battery, one is 'permanently' attached to the Meanwell power supply DC output, the other is a portable. i use 45 amp anderson powerpoles on 8awg wire to and from the load and source sides.

I set the voltage to 14.66, and connected the anderson powerpoles.

Both wattmeters registered an amp peak of 38.2 amps flowing into the battery, but when i looked it had already tapered to 32 amps. A minute later it was still accepting 25 amps.
2 minutes later it was still accepting 24 amps, and I started getting nervous.

I could detect no Heat building up on th casing or terminals, and hear no noises over the fans of my powersupply which run anytime it is plugged into either AC or DC.

After 8 minutes it was still accepting 22 amps. I really expected it to be less than this.
I wussed out and lowered voltage to 13.7v, and it was still accepting 9 amps when i came back to the computer to type these observations. I wil go back and raise voltage in increments to keep about 8 to 9 amps flowing into the battery until 14.66 is reached at battery terminals

I honestly expected less than 30 amps to instantly reach 14.66v and for amps to taper to the low teens in a few minutes.

The UB12180 states on its casing Not to exceed 5.4 amps of charging current
This Mightlymax AGM of the same exact dimensions and stated capacity, came with no instructions.

Does it have more thinner plates? Does it have a higher specific gravity of the electrolyte? Does it have significantly less resistance than the Ub12180?. Is this why it seemed to retain more voltage under discharge tha ni would expect, and accept way more amps for longer than I expected?

Unless I go back and find the battery melted and bulging emitting sulfur fumes. i am impressed!

If money were No object i would have gotten the Odyssey pc680, as these basically say there is no amperage limit, only voltage, but they want 129$ for one of those, and they are slightly larger for 18Ah and 3.4 Lbs heavier.
[-] The following 2 users say Thank You to sternwake for this post:
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Near the 1 hour mark recharging, with voltage set at 14.11, amps had tapered to 3.83. 9.5 Ah had passed through the wattmeters into the battery, some of that turned to heat.

I bumped voltage back upto 14.66 and amps rose to 9 then tapered to 4.65 in 20 seconds.

The digital thermometer simply placed atop the battery rose nearly 4 degrees but the body of the battery feels warm bt not hot to the touch. I should have had the IR thermometer on hand at the start. drat.

Edit. Ok IR thermometer shows the case temperature in the middle of the battery is 12 degreesF hotter than the air surrounding it, and I lowered voltage to 14.4, amps down to 2.8 and 10.5Ah claims to have bee returned to the battery, although some of that has obviously been turned to heat.

If batteyr temp keeps climbing I will keep lowering voltage. I expect it should level off, but my expectations have been wrong a lot so far.
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  • rvpopeye (01-08-2019), TWIH (01-13-2019)
2.5 hours into the recharge and amps have tapered to 0.71@14.4v, and battery temperature has decreased in the last half hour by 3 degrees F.

12.3Ah returned
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  • rvpopeye (01-08-2019)
@ 3 hours into the recharge, it was accepting 0.6 amps at 14.4v, and I decided to lower voltage to 13.6 and goto sleep.

7 hours later all ammeters read 0.00 amps at 13.61v, and i dialed voltage back upto 14.7. Amperage rose to 0.5 and quickly tapered to 0.24.

30 minutes later amps had tapered to 0.15 at 14.7v
30 minutes later amps had risen to 0.25 at 14.7v, and I removed the charger.

So the battery never tapered to 0.5% of capacity at absorption voltage, the amps beginning to rise again is a sign the battery cannot be charged anymore.

i have no Idea if the amperage and battery temperature would continue to rise, but I suspect so, and this could be the start of thermal runaway, which is of course dangerous, and perhaps why the chargers which come with most jumper packs are timid in their voltage algorithm.

So this appears to be different behavior than my Northstar AGM, which when new and held at absorption voltage, amps would eventually taper to 0.0x and seemingly never bounce off that floor.

I'll see where the voltage decides to rest at various times since it is now started to rest.

The 2 wattmeters indicated the battery had accepted 12.973 and 13.018 amp hours. The wattmeter during discharge indicated it had consumed 11.7xx AH correlated to the 12.973. The 13.018 wattmeter was reading the load of the second inline wattmeter.

Also the wattmeters seemed to agree almost exactly with the clampmeter in the sub 0.5 amp ranges, which is new behavior I cannot explain.
[-] The following 2 users say Thank You to sternwake for this post:
  • rvpopeye (01-08-2019), TWIH (01-13-2019)
Great write-up\follow thru! I enjoy reading through the whole process.
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  • S Cello (01-09-2019)

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