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AGM Maintenance Questions

lenr
Explorer II
Explorer II
I've replaced the OEM batteries (looked more like starter batteries then deep cycle) in our new fifth wheel with Trojan T-105 AGM batteries (4 each in 2 12 volt banks so voltages below are 2 in series.) I'd like these to last as long as possible due to cost, thus some questions. I also replaced the WFCO charger with a Samlex 50 amp charger. I picked that charger partly because I can set dip switches to determine the charging profile as I plug the trailer into shore power after a day of discharging.

1) Another thread implied that it was important to absorption charge AGMs at 14.4 volts. Trojan recommends that voltage. How important is this for battery health as opposed to 14.0 volts or 13.5 volts which the Samplex may be set up for?

2) Trojan recommends absorption at 14.4 v for a maximum of 2 hours. The Samlex may be set for a maximum absorption charge of either 4 or 8 hours. Obviously I have picked the 4 hour maximum, but will that be a problem exceeding Trojan's recommendation?

3) Since a maximum absorption charging time is probably related to heat, would 14.0 volts at a maximum time of 4 hours be safer? I do have a temperature monitoring probe from the Samplex installed in one battery bank.

4) Samlex recommends that the absorption mode (dip switch settable) be skipped entirely when load such as in an RV is attached, because the charger will never see a low current flow that signals the end of absorption and a switch to float (13.5). In other words, Samplex says to set the dip switches to go straight to float of 13.5 volts at the end of bulk. Because of other indications that an absorption period of 14.4 is important, I'm reluctant to do this. The Samplex will drop out of absorption when current drops to 5 amps. This is pretty easy to accomplish by not turning on many lights in the RV, and that triggers the drop to 13.5 float. So, should I just program the 14.4 absorption for max 4 hours, assume the temperature probe will protect the batteries, and trigger float by turning off lights when I see that my battery monitor says the batteries are 100%?

Thanks
11 REPLIES 11

MEXICOWANDERER
Explorer
Explorer
For the 50th time
Hear Ye!
Hear Ye!

IGNORE anyone who claims that AGM batteries lose water. They are opinionated with no education. PERIOD. Like listening to a taxi driver lecture about nuclear physics from the front seat.

AGM batteries hav e recombinant cell caps that only open when pressure in the cell reaches a critical level. 100.00000000000% of H2O is cooled then precipitates back into solution. And the cell remains 100.0000000% sealed.

I have never had an AGM battery vent Ever! unless a potential of 17 let's spell that SEVENTEEN volts is approached. Even after a full reovery (more severe than reconditioning) before and after precision weighing on my NIST certified platform scale revealed less than .25 ounce loss in the entire six cells. FOUR HOURS at 16.90 volts.

At a loss for words or positive pressure in your windpipe about these numbers?

Too lazy or obstinate to download and READ the Lifeline battery manual? Well then you would have made a short-lived bomb defuser.

No experience with your chosen subject area? They are always looking for taxi drivers.

I had to learn the facts by trial and error, before anyone printed a manual. I questioned the sanity of a spiral cell AGM battery manufacturer over the telephone from down here who said sixty amps divided by 12 group 31 batteries was "perfectly rational" for a cruising sailboat. The conversation was broadcast inside the vessel to a dozen skippers listening in. I had to fight my way up the ladder to get to a genuine engineer on that one.

I am not and never have been amused by fools pretending to be experts. They prey on the innocent. My built-in BS detector overloads my control on my temper.

BFL13
Explorer II
Explorer II
The temperature probe is just to adjust the charging voltage set on the charger. It does not protect from heat.

"Conditioning" is like equalizing--a rare need with AGMs and it is done at more like 15.5v. 14.4 will not do anything for that.

Longer time at 13.6 is not the same as time at 14.4. The higher voltage gets the electrolyte into the glass mat (or something like that. Whatever it was that Mex and PT said)

IMO you should forget anything the Trimetric says about percentage or SOC, and just use it as a volt meter, ammeter, and AH counter. Kill the auto reset. Reset the AH when the batts are truly full as measured by them getting down to 0.5/100 at 14.4v.

Never mind how long it takes to get down to that. Once down to that, change to Float voltage, not before.

PS, the whole Trimetric system for determining SOC is unsuitable for AGMs (and IMO for Wets too) You will think they are full and start a new cycle when they are not truly full. Plus whatever you set as your baseline capacity will be wrong, since it changes with temperature and battery condition. AGM (and Wet) capacity drops 15% between 77F/25C and freezing. Do you reset your capacity every six hours every day?
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.

lenr
Explorer II
Explorer II
Thanks for the replies--a few answers:

A) The 2 hour absorption limit comes from Table 6 on page 19 in section 5.2.2 in the Trojan users manual. I am trying to get a feel for the importance of this. Is it just a heat issue which I should be protected from with the temperature monitoring probe? Is it really a non-issue as long as the amps drop off as they should? My TriMetric has not indicated more than a 4% discharge (96%) left, and current drop off during re-charging seems to indicate that.

B) The charger is a 50 amp Samlex SEC-1250UL. One of my goals was to be able to set charging parameters with dip switches so things happen somewhat automatically as I travel, plug in overnight, travel, etc.

C) The OEM batteries (gone--gave them to my sons) had some obscure name and a starting current rating. They also didn't weigh much which all gave me low confidence of capacity or deep cycle ability. After my last experience with a WFCO boiling out a set of Trojan T-105 wet cells making a mess in the nose of the fifth wheel, I was determined to go to a sealed battery. Money always is part of a battery decision: while yours is unlimited, mine is, and the Trojan AGMs met my needs. By the way, the MotorCraft starting batteries in my truck still seem to be wet cell--I add distilled water to them periodically.

So I'm still trying to clean answers from the replies:

5) Do I need to run 14.4 volts to "condition" the batteries back to full capacity? Or, will a long time at 13.5 do the job?

6) If I exceed 2 hours at 14.4, am I in dangerous territory of gas discharge? Or, is dangerous only if the discharge went down to 50% discharge? Or, is it not dangerous at all because the Samlex will slow down if it sees a Temperature rise?

I am going to look for time to do a run-down/charge-up test to learn how my installation works. Thanks, again, for the replies.

MEXICOWANDERER
Explorer
Explorer
There is more H.S. surrounding battery types than any 20 riding stables.

  • Use the same radial grid layout
  • Add .010" thickness to the plates
  • Slap on a different label
  • And suddenly Clark Kent is wearing blue leotards and a cape that would have done Liberace proud.


If a group 24 advertises more than 450 CCA, a group 27 more than 500 CCA, a 31 600 CCA [COLOR=]It's a fraud!!! A scale and a carbon load test do not lie.

MARINE my ass. Grade E to S plates (cured paste) with standard .040" standard paste, different terminals, less warranty and higher price is a sucker deal. Period. I can spend seven hundred dollars for 4 Rolls & Surrette group 27 batteries, and they will outlast and outperform 4 mass-market so-called Deeeeeeeeeep Cycle batteries by a factor of four to one lifespan. Unless obsolescence is a factor, if you didn't come up with the right answer then join the crowd.

RJsfishin
Explorer
Explorer
And at the end of all your spending money on hi $ batteries and way overthinking the charging aspect of it all, you are going to find, as many have already, that your hi $ Agms will not last any longer than the cheap ole LA 6volts from cosco. And when using a PD converter charger, batteries just don't use any water. Under RV deep cycle use, AGM batteries will dry out in a relatively short life, and no way to replace water. So, at least do your expensive overpriced AGMs a favor and charge them w/ a PD charger,.......the only charger that has real technology built in !!
Yeah, lets talk abouy those that don't have a clue ???
Rich

'01 31' Rexall Vision, Generac 5.5k, 1000 watt Honda, PD 9245 conv, 300 watts Solar, 150 watt inv, 2 Cos 6v batts, ammeters, led voltmeters all over the place, KD/sat, 2 Oly Cat heaters w/ ox, and towing a 2012 Liberty, Lowe bass boat, or a Kawi Mule.

wa8yxm
Explorer III
Explorer III
I have one question of the O/P
You said the OEM batteries looked more like "Starting Batteries than Deep Cycle"

Since the only visible difference is the battery model number .. How can that be?

Now I do understand that most starting batteries are Valve Regulated SLA batteries (Maintenance free) including all AGMs.. And most are in a black rectangular "Box" though other colors are possible.

And MOST deep cycles today are GC-2 Flooded wet (With caps so you can add distilled) But I am old enough to remember flooded wet cell starting batteries.


That said the most common 12 volt "Deep Cycle" is really a Marine Starting battery with lip service to deep cycle. you can safely take it down to around 75% as opposed to 80 for Starting and 50 for True DEEP CYCLE
ANd you can get Valve Regulated SLA DEEP CYCLES as well. So the appearance is identical.
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times

MEXICOWANDERER
Explorer
Explorer
After meeting and talking to young pencil necks at Trojan, you can bet your sweet butt they pale In comparison to Concorde's .

time2roll
Nomad
Nomad

Lwiddis
Explorer II
Explorer II
“Trojan recommends absorption at 14.4 v for a maximum of 2 hours.”

Why would you trust Trojan enough to buy their batteries and then not follow their recommendations?
Winnebago 2101DS TT & 2022 Chevy Silverado 1500 LTZ Z71, WindyNation 300 watt solar-Lossigy 200 AH Lithium battery. Prefer boondocking, USFS, COE, BLM, NPS, TVA, state camps. Bicyclist. 14 yr. Army -11B40 then 11A - (MOS 1542 & 1560) IOBC & IOAC grad

MEXICOWANDERER
Explorer
Explorer
One single Megawatt with fixed voltage would cure this problem. I put a Lifeline to the test. 14.40 volts for 2 weeks 24/7

3°F gain in heat
Amperage flow in single digits milliamps

The MW would make a great camping and 100% full unit while the Samlex would take over the remaining duties.

Sixty dollars. The average whiner about this expense drinks that much synthetic beer in a weekend attempting to block out any remaining contact with reality

BFL13
Explorer II
Explorer II
Ignore the battery monitor's idea of when the AGMs are full. EG the Trimetric has a 1-2% of capacity as " full" except they require you to set an AH capacity. Unfortunately that capacity is highly variable with temperature and over time with age and condition of the batts. So it is fairly bogus right there, plus AGMs require amps to taper to 1/2 of 1% at 14.4v before they are full. So the Tri is out to lunch on that too.

With a Tri, you just use your AH counter and your own existing estimate of bank capacity and do your own math for the SOC. Also do a cross check with voltage per SOC for your battery's spec allowing that you can't get quite to actual "resting" voltage while camping with always some low amp RV draw. You know when it is at its lowest draw, so use that--close enough! (ie wait till after the furnace is off for now and turn off the lights.)

Sometimes the AH count and the voltage don't "match" for what the SOC should be. This is a clue that you need to do some checking on the situation. Sometimes that is because the AH counter needs resetting. You must kill the auto reset if you have solar for instance.

I never try to get the AGMs or even the Wets truly full when camping off grid. You can't run the generator that long. On solar you run out of daylight. Just do what you can (50-90s eg) and wait till you have shore power and all kinds of time. Now you can go for the 0.5a/100AH using your Tri as the ammeter for noting when you get down to that 0.5a per.

It will take hours and hours to get there. The AGMs will not heat up doing that.

It sounds like that Samlex charger with its options will not do what you need, and also IMO you are mis-interpreting what Trojan says.

See 5.22 for AGMs here: Nothing there about two hour limits! It says absorption ends when it gets down to 0.5. No time limit.

https://www.trojanbattery.com/pdf/TrojanBattery_UsersGuide.pdf

Good thing you are on here asking, though. Proves that you have a clue! 🙂
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.