Using a flooded starter battery for dual battery install and some deep cycling

[OllieChristopher]

As some of you know I'm doing a dual battery install on my 05 GMC sierra:

Dual battery install 05 GMC Sierra with pics

Hi guys I'm new here. Thought I would share some pictures and my procedures for a dual battery install. This is model specific but can cross over to many other makes and models. First a little background. I have been a lurker here for many years. I'm getting to a point in my life to do some...

expeditionportal.com

I'm running the numbers in my head and just now decided to just pop in another AAA flooded starter battery (group 78) of the same kind I replaced back in July 2020. Reason being it's only 140.00 with a 3 year replacement warranty. 2 AGM deep cell batteries are going cost close to 600.00 and I'll be throwing away a perfectly good starter battery.

This is not the best choice but budget wise It's a smart one. 36 months for a 140.00 battery is less than 13 cents a day and I keep an already perfect 6 month old battery. To get 13 cents a day for a AGM set of batteries, I would have to keep them for almost 13 years. It's a no brainer.

This is going to be a real world experiment to see what happens when I deep cycle this battery. As often as I go out I doubt I'll cycle it down more than a few dozen times a year. For comparison my last flooded AAA battery in my truck lasted over 5 years. Of course it was not deep cycled. I'll be happy to get 3 years out of this set (even if I use the warranty). I have AAA roadside so they bring the battery to you and install free of charge anywhere in the US.

I don't know much about using a relay system other than I prefer to keep my "battery bank" the same. I'm not going to get so anal as to match the exact date of batteries. Same battery type 6 months apart should be good enough for my use.

I also am using the Victron 75/15 charge controller to keep them topped off when my truck is parked. Cool thing about the controller is I can keep track the battery cycles and charge.

The reality is I'll be running an electric cooler, some led lights in the bed of the truck, charging phones/laptop, maybe a plug in air compressor once in a while. I'm also going to have a 100 - 200 wats solar and a small inverter gas generator for aux charge power to system when truck is parked for camping. Camping trips are normally just a few days.

I'm expecting to not go much past 50% discharge on the house battery. I also keep my batteries on a "tender" when my truck is parked at home. Has anyone ever done this with flooded start batteries? If so how long did they last before replacement? FWIW, while these are a "maintenance free" battery, I can add water to them and keep them topped off as needed.

I'll keep up with this thread and let you know the numbers as time goes by. I predict that I'll get at least a solid 18-24 months out of the battery set before I use the warranty.

 

[Joe917]

So you are going to ruin a starter battery by deep cycling it then replace it on warranty, and you think this is a good idea...?
Just buy a deep cycle FLA.

 

[Buddha.]

I don’t think the mismatched age matters if they are only connected when charging.
My two batteries aren’t even the same size.

 

[OllieChristopher]

So you are going to ruin a starter battery by deep cycling it then replace it on warranty, and you think this is a good idea...?
Just buy a deep cycle FLA.

I'm not so sure I will be replacing it under warranty for what I'm using it for. All batteries are going to be ruined at some point regardless of type. Have you ever used a starter battery for occasional deep cycling? What kind of life did you see from it?

I'm looking at it strictly by math and budget. 13 cents a day for guaranteed 3 years or spend 13 cents a day hoping to get 13 years. With 2 batteries the chances of both of them dying at the same time are not probable.

I'm very aware that for a hard core rig that will be seeing weeks off the beaten path my choice is not so smart. My truck is a daily driver that is being used as an occasional rig for hauling my motorcycle and camping out.

Once I kill off the warranty on my start batteries then I'll look at the AGM or maybe even LiFePO4 batteries will be available by then. Group 78 deep cycle batteries are only available in AGM style currently. Flooded deep cycle batteries cannot be fitted in my trays without a lot of modification.

 

[john61ct]

Very foolish move, no upside all downside.

A pair of Deka GCs is not going to cost much if at all more per actual usable Ah

and will last 5x maybe 10x the cycles

because A they are actually designed for deep cycling, and B EPM is a great manufacturing company with excellent engineering, QC and customer support.

Also (maybe even better) Trojan, U.S. Battery, Crown and Superior

they just cost a bit more depending on your location.

Rolls/Surette is tops, pricing to match.

There are no other good FLA makers in NA for deep cycling.

 

[vtsoundman]

I'm running Sam's club Group 31 AGM Deep Cycle Duracell 100-110Ah as my starting battery. Plenty of CCA to turn any engine over. Been deep cycling it for several years now (4-5 yrs now)...$187. Runs my winch too.

I'll be able to have fresh Batts avery 4-6 yrs and still be way way ahead of fancy LA AGM brands.

Prior to that, it was a Die-hard Platinum Grp 34 AGM...lasted for 7 yrs before it started showing its age (still perfectly fine however - lost about 30% or so of usable caoacity). When new, it was far from a $300 AGM/Northstar/fancy brand.

$300 for an AGM is nuts. Expensive LA batteries do not pay for themselves... especially under the hood. Heat kills batteries!

FLA is a waste of money as well...and makes a mess. Cheap, good AGMs exist (you're within spitting distance at your FLA prices).

My Jeep also has a 100Ah Ubs121000 AGM under the back seat....it was $165 when I bought it. Going on 4-5 yrs, truly deep cycling it (to 20-30%). It's charged via CTEK DcDc, solar....it's working great as well.

I keep all my Batts on 3A Battery Tenders at least 1x month for several days at a time. Avoids PSOC early death.

Starting /high current FLA do not cycle well. You're taking the time to keep it properly charged...go buy an AGM from Sam's club.

You're wasting money with your proposed sol'n. Get a separation relay and a proper 100 Ah battery ( if underhood, Sam's Club)...two smaller LA batteries does not equal one big one when used in proper isolated dual batt systems. Run the new starting batt into the ground as a starting batt. When it does, swap in a cheap Sam's Club ******.


Edits...lots of them.


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[OllieChristopher]

Very foolish move, no upside all downside.

Why so negative John?

Time will tell and be the true indicator of battery life. For me it's worth spending 140.00 vs a lot of modification or cost to get a deep cycle setup that I will not use to it's full potential. As stated once I

Internet opinions aside, I have actually seen flooded car batteries being used for deep cycle camper and trailer power sources and do just fine for quite a few years. In the 90's we used just cheap interstate flooded starter batteries in fleets of generators that would set for long periods, go dead, recharge dozens of times and last 3-5 years or more. Same goes for the small hydraulic drilling rigs that relied on the same bank of starter batteries cycled daily for setting power poles, and winches/hydraulics on our tilt back trailers I fabricated.

 

[vtsoundman]

Made some edits to my post...

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[john61ct]

What modification or additional cost?

I'm not being "negative" I'm trying to help you, letting you know there is literally no reason afaict to go that way, and plenty of reasons not to.

Have you even priced the GCs?

Of **course** if you're happy with the result you will get, go for it! 3-5 years is nothing to brag about.

We're only talking here about wasting maybe $50-100 per year, so no big deal.

 

[john61ct]

@vtsoundman sorry but nope.

This convo has nothing to do with cranking, deep cycling is a completely separate category. But as you say the latter can handle the former, just you really should keep them separate except while charging.

Deep cycling FLAs are **much** cheaper and last linger and more robust and easier to care for than deep cycling AGM.

Deka / EPM makes Duracell, yes fantastic value for FLA GCs

that same $187 is the ballpark for 220Ah @12V

but their AGM are no great shakes compared to Odyssey, Northstar and Lifeline. Same as Trojan, and Interstate is not even a maker, just relabels JCI.

AGMs outside of those three are not worth considering for deep cycling, and certainly any AGM is poor value compared to the FLA I'm talking about.

5-8yrs should be the goal even for those cheapies, other FLA can go 10+ easy, seen 14yrs, and that is judging EoL proactively, 70-75% or so SoH.

 

[vtsoundman]

Very foolish move, no upside all downside.

A pair of Deka GCs is not going to cost much if at all more per actual usable Ah

and will last 5x maybe 10x the cycles

because A they are actually designed for deep cycling, and B EPM is a great manufacturing company with excellent engineering, QC and customer support.

Also (maybe even better) Trojan, U.S. Battery, Crown and Superior

they just cost a bit more depending on your location.

Rolls/Surette is tops, pricing to match.

There are no other good FLA makers in NA for deep cycling.

We've debate this one before...

Very few Overlanders actual cycle their Batts to death, most calendar them out...or let them die early from PSOC (strictly rely on vehicle alternators).... I work out of my rigs and run all sorts of loads and run minimal solar. (Long before van life...but much less recently with Covid, ugh). I'd consider my usage as much harder than avg, but not quite a full-timer. The cheap AGM Batts work awesome.

The math doesn't support expensive AGMs in most vehicle applications - starting or house. (except maybe boats. Off grid solar is a diff animal).

$187 every ~5 years beats $300 every 7yrs...and I'll have more usable Ah with fresh batts. Going to the back country with a 7yo starting battery is somewhat foolish anyways. A dead house battey is an inconvenience...a catastrophic dead starting battery is not.

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[john61ct]

I am clearly stating the expensive AGMs that are required for good deep cycling performance are not good value.

Cheap AGMs you are talking about are not cheap compared to those Deka and other quality FLA deep cycling GCs.

And no one is talking about Starters here.

Plenty of scenarios where House is mission critical, even life threatening.

For weekenders barely leaving the pavement then of course doesn't matter.

Same for those happy to replace more often than would be needed if they bought smart in the first place.

Not saying your way doesn't work

just that it isn't optimal, and I hate seeing false info spread as if facts.

 

[vtsoundman]

@vtsoundman sorry but nope.

....


but their AGM are no great shakes compared to Odyssey, Northstar and Lifeline. Same as Trojan, and Interstate is not even a maker, just relabels JCI.

AGMs outside of those three are not worth considering for deep cycling, and certainly any AGM is poor value compared to the FLA I'm talking about.

5-8yrs should be the goal even for those cheapies, other FLA can go 10+ easy, seen 14yrs, and that is judging EoL proactively, 70-75% or so SoH.

Your numbers sort of jive for stationary large cell/capacity FLA app locations, but not vehicle. No way.

10-14yrs FLA in a realistic vehicle app that still has usable capacity at 70-75 of original Ah??? Sorry, but that's a little hard to believe.

As an outlier for an RV parked in a coastal climates that never moves and cycle 20x/yr... sure, but not 70-75%. 10-14yrs for a ln oversized bank where a 50% loss won't be noticed....sure, maybe. On a large format cell in a boat, maybe... stationary UPS, maybe...10y/o FLA in a typical Overlander, nope.

Road shock and vibes, hot temps, etc - all take their toll on LA, regardless of brand, type.


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[vtsoundman]

...

just that it isn't optimal, and I hate seeing false info spread as if facts.

That's a mighty big statement...

John, generally your advise is solid, but come on - What was that again? 10-14+yrs with FLA in a vehicle app and a 75% SoH? Ok...your numbers are growing with time/posts.

Golf carts and LA based small electric vehicles will cycle out their Batts every 4-7 yrs or so, and that's pushing it, FLA or AGM... If 10-14 were even remotely possible Lithium economics would have taken a lot longer to pencil than it did. Forklifts...another industry that would go nuts for a 10-14yr FLA 75% SOH...

The reason I cite these examples - all can run larger format FLA cells that should be capable of the lifetimes you claim...but don't actually see that on an ongoing basis.

Lithium batts in overlanders is taking over - it's been over for LA in my professional life for several years now (mobile and stationary apps alike). If 10-14 yrs were even remotely viable, I'd be knee deep in acid...

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[Buddha.]

Have you even priced the GCs?

6v golf cart batteries are great but OP doesn’t have room for an extra pair of largish batteries under the hood of his pick up truck.