A Few Auxiliary Battery Questions

[Nailhead]

I have two Duracell 2018-vintage gr 31 AGM’s for house batteries, and they just don’t seem to get fully charged on the road.

They charge off a Powermaster 100A 12si alternator through a Victron isolator at 13.7 to 14.2 v (IIRC; the truck is quite a ways away from where I’m working right now) as indicated by the Holley Sniper display. The cables from the isolator to the battery box are maybe 6’ long, and are 4ga with hydraulically crimped copper lugs on both ends.

The batteries generally end up at 12.7 volts, which only illuminates three of four segments on the state-of-charge portion of my Aims Power 1200w inverter/charger display. If I hook up my Renogy 200w suitcase or the charger, the batteries will eventually top off.

The problem I’m having is that they’ll no longer provide enough voltage to start the Suburban 12000 btu furnace in the camper, which is in the top three of the most valued features in the camper. If I run off the shoreline, the furnace will fire right up. It did so just fine off the batteries two years ago without a top-up, but not now.

Have these batteries aged out of the workforce, or is this problem charging-system related? The batteries are only 6 years old, and have not seen a whole lot of use.

Not interested in lithium batteries, BTW: too expensive and my charging system is not compatible with them.

Thank for any insights.


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[DiploStrat]

If it worked two years ago and now it doesn't, and nothing has changed, and you only have a 100A alternator, and the batteries date from 2018 ...

-- The batteries have aged out, especially if they did not get a full absorb cycle ever two weeks or so. (That would require solar or shore power charger with the correct profile.)

-- A pair of Battle Born or similar would probably drop right in, as long as your isolator has the ability to limit charge to no more than about 75% of your alternator's max output. Most modern lithium iron drop in batteries want an absorb voltage of 14.0 to 14.5v. Usually a two hour max.

-- Buying new AGM would not be money well spent. Lithium iron batteries (with a decent BMS) are simply better in every way. You would drop your weight by at least 25% and double you effective output - especially as the lithium iron batteries run at about 13.5v - your appliances will love the extra volts.

 

[jonyjoe101]

14.2 volts is too low for AGM batteries. I have 2 high performance agms that require 14.7 volts to fully charge. At least they should be charged to 14.4 volts like lead acid. One of my agms I bought in 2013 and currently using as my start battery, still cranking my van everyday but I have a seperate dc to dc charger to top it off to 14.7 volts at least once a week.
Even your solar is probably not topping them off to 14.4 volts due to voltage drop and most solar controllers aren't properly calibrated (they read higher than the battery terminals).
You need to measure the battery voltage at the terminals to see if they are even reaching 14.4 volts, if not they are not getting fully charge and that is bad for the battery and will loose capacity real quick.
I googled to see what the max charge voltage for duracell grp31 are but couldnt find it. But the minimum is 14.4 volts for most agm's. 13.5 to 14.1 volts would be a float charge. At 14.2 volts the battery is barely getting a float charge.
Get a good charge on them and hopefully it would be bringing them back to full capacity. But if the voltage has dropped below 12.1 volts too many times during use, they might not be able to fully recover. If they gone below 11 volts during use thats usually not good and damage might be permanent from chronic undercharging.

 

[Nailhead]

If it worked two years ago and now it doesn't, and nothing has changed, and you only have a 100A alternator, and the batteries date from 2018 ...

-- The batteries have aged out, especially if they did not get a full absorb cycle ever two weeks or so. (That would require solar or shore power charger with the correct profile.)

-- A pair of Battle Born or similar would probably drop right in, as long as your isolator has the ability to limit charge to no more than about 75% of your alternator's max output. Most modern lithium iron drop in batteries want an absorb voltage of 14.0 to 14.5v. Usually a two hour max.

-- Buying new AGM would not be money well spent. Lithium iron batteries (with a decent BMS) are simply better in every way. You would drop your weight by at least 25% and double you effective output - especially as the lithium iron batteries run at about 13.5v - your appliances will love the extra volts.

Thank you for the reply.

“Aged out” is what I suspected, and they have sat long periods without a charge, through several winters. I didn’t know topping off the charge regularly was a good idea. Oh well.

As for the lithium batteries, though I do appreciate the advice, the buy-in as I’m aware of it ($1200 x 2 for the batteries, plus whatever a BMS might cost) is prohibitive and not something I can rationalize.


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[Nailhead]

14.2 volts is too low for AGM batteries. I have 2 high performance agms that require 14.7 volts to fully charge. At least they should be charged to 14.4 volts like lead acid. One of my agms I bought in 2013 and currently using as my start battery, still cranking my van everyday but I have a seperate dc to dc charger to top it off to 14.7 volts at least once a week.
Even your solar is probably not topping them off to 14.4 volts due to voltage drop and most solar controllers aren't properly calibrated (they read higher than the battery terminals).
You need to measure the battery voltage at the terminals to see if they are even reaching 14.4 volts, if not they are not getting fully charge and that is bad for the battery and will loose capacity real quick.
I googled to see what the max charge voltage for duracell grp31 are but couldnt find it. But the minimum is 14.4 volts for most agm's. 13.5 to 14.1 volts would be a float charge. At 14.2 volts the battery is barely getting a float charge.
Get a good charge on them and hopefully it would be bringing them back to full capacity. But if the voltage has dropped below 12.1 volts too many times during use, they might not be able to fully recover. If they gone below 11 volts during use thats usually not good and damage might be permanent from chronic undercharging.

Thank you for the information.

As I said, I’m not real sure of the charge system voltage, because I can’t remember it. Important info, to be sure, but my fading memory seems to give little consideration to the importance of the information it deletes.

I’ll take a look at that voltage this week and do the various voltage measurements you recommend, get a better idea of what’s going on, and report in again.


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[DiploStrat]

Some random thoughts, having had AGM and now having built my own lithium iron bank.

-- Lead acid batteries (AGM) are actually much harder to live with as they demand a full, plate shaking charge, ideally once a week.

-- Lead acid batteries HATE sitting at less than full charge; they love to be floated. If (and you shouldn't) you stay with AGM, make sure that you have a way to keep them on charge when your truck is in storage. In my case, I have a dedicated B2B that keeps my starter batteries charged from the lithium iron camper bank. There are many ways to do this. When my set up was all AGM, I used an intelligent relay and that assured that my camper bank kept the starter batteries charged.

-- Lithium iron batteries prefer to sit at about 50% charge, indeed most of the float settings on chargers may be a bit high for a truck that is in storage and does not have the usual loads of refrigerator, fans, etc.

Finally, you might try a reconditioning charge if your shore power charger will do it. Dig through the Lifeline battery tech manual to find instructions: https://lifelinebatteries.com/wp-co...F-Lifeline-Technical-Manual-Final-5-06-19.pdf See 5.5, page 21.

Good luck! (And do look at Battle Born or similar. They have good built in BMS's and are pretty close to plug and play.)

 

[Nailhead]

Some random thoughts, having had AGM and now having built my own lithium iron bank.

-- Lead acid batteries (AGM) are actually much harder to live with as they demand a full, plate shaking charge, ideally once a week.

-- Lead acid batteries HATE sitting at less than full charge; they love to be floated. If (and you shouldn't) you stay with AGM, make sure that you have a way to keep them on charge when your truck is in storage. In my case, I have a dedicated B2B that keeps my starter batteries charged from the lithium iron camper bank. There are many ways to do this. When my set up was all AGM, I used an intelligent relay and that assured that my camper bank kept the starter batteries charged.

-- Lithium iron batteries prefer to sit at about 50% charge, indeed most of the float settings on chargers may be a bit high for a truck that is in storage and does not have the usual loads of refrigerator, fans, etc.

Finally, you might try a reconditioning charge if your shore power charger will do it. Dig through the Lifeline battery tech manual to find instructions: https://lifelinebatteries.com/wp-co...F-Lifeline-Technical-Manual-Final-5-06-19.pdf See 5.5, page 21.

Good luck! (And do look at Battle Born or similar. They have good built in BMS's and are pretty close to plug and play.)

I am not discounting any of the information you’ve provided on lithium batteries; indeed, I have batted the idea around several times UNTIL price came up. I simply cannot justify the breathtaking expenditure, no matter what features are included. This is a recreational vehicle, after all. These two AGMs cost less than $300, and it’s looking like my own ignorance caused their apparent demise. I’m willing to try it again armed with the knowledge gained here, because I can buy a lot of these for the price of two BB’s ($1850).

 

[DiploStrat]

Ran AGM's for years. Lifeline makes a great product. Read and understand the manual and you will be good for at least five years.

All the best!

 

[Dave in AZ]

I am not discounting any of the information you’ve provided on lithium batteries; indeed, I have batted the idea around several times UNTIL price came up. I simply cannot justify the breathtaking expenditure, no matter what features are included. This is a recreational vehicle, after all. These two AGMs cost less than $300, and it’s looking like my own ignorance caused their apparent demise. I’m willing to try it again armed with the knowledge gained here, because I can buy a lot of these for the price of two BB’s ($1850).

I don't understand why you keep saying the LFP batteries are expensive, your 31 Agm duracells are only 87 Ah. You can buy a 200Ah LFP, giving you 1.5x the Ah and waaay more actual usable Watt-hrs, for $420, and a self heating one for $575. There is zero reason to pay 10x market price for BattleBorn. This is like pricing your daily driver based on a Lamborghini price.

 

[DiploStrat]

The only reason to buy Battle Born, Lithionics, etc., is the known quality control - the BMS will work when you need it to - and the long guarantee. Also, if you are new to this stuff, they are more likely to be plug and play. Lithiums are coming in easy to mount packages these days - traditional shape and things like the "Game Changer" with tabs on all sides.

Good comment on capacity. Lead acid usually has about 50% usable capacity for longevity. Lithium iron runs that way up above 80%. (Battle Born claims 100%, but they simply make their batteries about 20% over the advertised capacity.)

Of course, are you really gonna keep that camper for ten years? By then, you will want a flux capacitor.

 

[Nailhead]

I don't understand why you keep saying the LFP batteries are expensive, your 31 Agm duracells are only 87 Ah. You can buy a 200Ah LFP, giving you 1.5x the Ah and waaay more actual usable Watt-hrs, for $420, and a self heating one for $575. There is zero reason to pay 10x market price for BattleBorn. This is like pricing your daily driver based on a Lamborghini price.

Because the BB was the subject of the conversation at $925?

The Duracells are 105ah, BTW.

If you’ve got some information to share in a civil and respectful manner I’m all ears; it’s why I started this thread, after all. If those simple stipulations don’t work for you, save your energy and go elsewhere.


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[Dave in AZ]

Because the BB was the subject of the conversation at $925?

The Duracells are 105ah, BTW.

If you’ve got some information to share in a civil and respectful manner I’m all ears; it’s why I started this thread, after all. If those simple stipulations don’t work for you, save your energy and go elsewhere.


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Not sure what is setting off your sensitivity... your opening post did NOT mention battleborns, you merely stated Lithium batteries were too expensive, so you weren't interested. Later, battleborns were mentioned, but my point is your very 1st opening post: in fact, lithium iron phosphates are NOT too expensive, and you can get significantly more Watt-hrs for the same price than AGMs. I looked up the sprcs on your Agm duracell T 2 sources, they are not actually 105Ah. There rating for 25A is 210 minutes. This is 87.5 Ah. An agm can only use 70 to 50% of its named Ah, pretty much.

So... are battleborn a requirement for you, if you went lithium? As far as I can read here, they were just randomly mentioned by someone, I see 95% of folks posting here picking something else, and have watched 20 videos comparing BB to Epoch or SOK, and finding them lacking for the price. I feel you have been led a bit astray on LFP pricing, and that an actual replacement cost would be $450 to $600 for a better battery and more power. Please take a look at other LFP vendors before writing them off.

 

[chet6.7]

Check out the Will Prowse youtube channel, he likes a LiTime trolling motor battery as a budget lithium.

 

[jonyjoe101]

agms will get the job done. I use all 3 agm, li-ion and lifepo4. The only difference is agms require proper charging everytime. Need to be fully charged everyday to max voltage recommended (including compensating for cold and hot weather). My start battery is a 13 year old agm and its still running strong.
The lithium batteries are more lenient concerning charging, you can charge every other day, charge them to 70 percent etc.
I only moved to lithium because my agm's werent lasting long, after moving to lithium was when I found out about voltage drop. My agm's weren't lasting because my charge controller was only charging them to 14 volts. I was happy with my agm's they ran my fridge and all my electricals.
Once you move to lithium its hard to go back to agm's, but the agm's worked good when they where fully charged but if constantly undercharge they eventually loose capacity.

 

[Buddha.]

I have two Duracell 2018-vintage gr 31 AGM’s for house batteries, and they just don’t seem to get fully charged on the road.

They charge off a Powermaster 100A 12si alternator through a Victron isolator at 13.7 to 14.2 v (IIRC; the truck is quite a ways away from where I’m working right now) as indicated by the Holley Sniper display. The cables from the isolator to the battery box are maybe 6’ long, and are 4ga with hydraulically crimped copper lugs on both ends.

The batteries generally end up at 12.7 volts, which only illuminates three of four segments on the state-of-charge portion of my Aims Power 1200w inverter/charger display. If I hook up my Renogy 200w suitcase or the charger, the batteries will eventually top off.

The problem I’m having is that they’ll no longer provide enough voltage to start the Suburban 12000 btu furnace in the camper, which is in the top three of the most valued features in the camper. If I run off the shoreline, the furnace will fire right up. It did so just fine off the batteries two years ago without a top-up, but not now.

Have these batteries aged out of the workforce, or is this problem charging-system related? The batteries are only 6 years old, and have not seen a whole lot of use.

Not interested in lithium batteries, BTW: too expensive and my charging system is not compatible with them.

Thank for any insights.


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I don’t know if you’ve looked at the price of AGMs lately but I don’t think they’re as cheap as they used to be.