Seeking dual battery advice

[CharlieS]

Hi there fellow mudders. I'm looking for some guidance.

I have a '13 LC and I am putting a dual battery setup in it. I have the Slee primary and auxiliary trays, and am using a Redarc BCDC1225 for charging and a Redarc BCI for self jumping.

The Slee primary tray is designed to fit an Interstate 31P-AGM7 for starting and a group 35 for the auxiliary.

I am not very knowledgeable about batteries, and figured that would be enough to go on at my local Interstate battery dealer. It didn't work out though, they didn't stock the 31P-AGM7 and they didn't have any group 35 batteries in stock. Everything is special order.

So, for anyone with the Slee trays, which batteries are you running, and would you recommend them?

Should the auxiliary battery be deep cycle? Is AGM important?

Thanks in advance for anything you are willing to share.

 

[OregonLC]

I'm a fan of the X2Power from Batteries +. They're a rebadged Northstar. Not absolute top shelf like Odyssey but they're a great value brand. Having the BCDC will keep the AGM in top shape.

 

[Sandroad]

If you need solid info right away and don’t feel like waiting for responses to your question, just use agm as the search term on this forum and you’ll get several (at least 15) pages of threads on the topic of batteries.

The second battery should definitely be deep cycle. AGM is not important. If your local Interstate dealer didn’t have a deep cycle group 35 in stock, find another dealer. That’s a very common size In both terminal configurations.

 

[TeCKis300]

Sounds like you have some great components going in.

AGMs are nice batts. Will work great though not necessarily ideal underhood with the higher engine bay temps. I believe the redarc charger has temp compensation to protect the batt in higher temps.

Flooded lead acid is ideal underhood. May trade some usable capacity over AGM though.

 

[Fisher23]

I did a lot of research on here and there is another forum group for batteries and power on here.

There are also some good youtube videos on the subject.

If you are going to use that 2nd battery for winching and tie it in with your main, then you are best to run a non-deep cell battery.
If you are going to keep it isolated and run a fridge and aux gear then you are best with a lithium. The lithiumcharges faster and you can deep cycle way more that the 300 times a deep cell can go. Lithium are good 1000+ and some 3000+ cycles.

Same price as a deep cell if you look around.

 

[cboyd]

Another fan of X2 here. I run them for primary and aux on my 100 series. Eventually I’ll be doing the same on my 200.

Aux /house battery should definitely be and AGM deepcycle

As for the comments in lithium above - just be careful of what temps you’ll be running in. LiFePo4 cannot be charged under 35F without damage to the cells. The BCDC knows this, but you need a battery with a temperature controlled BMS.

I’m planning to add a lithium to the rear of my 100 for house / solar duties and let the two batteries under hood be for winching and backup to starting, along with some cockpit loads (nav, radios, etc) to keep the alternator happy.

 

[Markuson]

Lots of “absolutes” (strong statements of fact) tend to show up in battery threads...

In my opinion, it’s a much fuzzier question with a zillion end use style factors that change the “answer” significantly.

Most battery advice posts need to say, “it depends...” somewhere.

Because.... It really depends on _____, _______, and often ______ & ______, too!

 

[RET2]

Well said @Markuson, what has worked for me is regular monitoring and replacement every 2 yrs.
I use the cast offs in farm equipment on my ranch. This also keeps my trickle chargers employed.

 

[Chrisleduc1]

Will the BCDC1225 charge the starting battery as well? It "seems" that the stock alternator does not like charging the AGMs?

 

[OregonLC]

Will the BCDC1225 charge the starting battery as well? It "seems" that the stock alternator does not like charging the AGMs?

Two things going on here. AGMs like their charging profile to be at 14.7-14.8. The alternator won’t get there. Nor does it have logic to taper off when the battery has reached full charge. The BCDC will adapt its output to the battery profile you specify regardless of input voltage or source. So it will always be working to maintain the battery in its optimal state. The alternator isn’t programmed to do that. It wants to yeild the best fuel economy while providing sufficient charge for starting the truck. The alt knows nothing about caring for a deep cycle AGM.

Your other question regards mixing battery types. I don’t believe the BCDC will do this but you would have to check the manual. Regardless, I would suggest you leave the starting battery alone and let the OEM bits worry about doing that job and let the BCDC work on your house battery. For the starting system you want rock solid reliability and tinkering has the likelihood of inducing complications.

 

[Fisher23]

The 1225 charges the agm, lithium and deep-cell well. the 1225 is 25 amp, they also make a 40 and 50 amp.

Since I use my front aux for winching, I put a 35 AGM non-deep cell in the front. So I have two 35's in the front.

Then I have a 3rd battery a lithium in the rear for running the fridge which is isolated. I forget the make but it starts with a "v" and it's green normally used in the medical field. It's 80 amp hours and these you can find for around $150. Eventually I'm going to hook a solar panel to this 3rd one.

 

[Chrisleduc1]

Two things going on here. AGMs like their charging profile to be at 14.7-14.8. The alternator won’t get there. Nor does it have logic to taper off when the battery has reached full charge. The BCDC will adapt its output to the battery profile you specify regardless of input voltage or source. So it will always be working to maintain the battery in its optimal state. The alternator isn’t programmed to do that. It wants to yeild the best fuel economy while providing sufficient charge for starting the truck. The alt knows nothing about caring for a deep cycle AGM.

Your other question regards mixing battery types. I don’t believe the BCDC will do this but you would have to check the manual. Regardless, I would suggest you leave the starting battery alone and let the OEM bits worry about doing that job and let the BCDC work on your house battery. For the starting system you want rock solid reliability and tinkering has the likelihood of inducing complications.

Is there a way to make the BCDC charge both starting and house?

 

[Fisher23]

The alternator charges the starting battery. The BCDC charges the aux. isolated batteries and can also tie into a solar panel/s and act as a solar controller.

 

[OregonLC]

Since I use my front aux for winching, I put a 35 AGM non-deep cell in the front. So I have two 35's in the

I might suggest you revisit this strategy. Our alternator is 150A (180?) vs the 25 of the BCDC. Winching consumes a ton of power and you want as much of that to come from the alternator as possible. Most setups run the winch to the starting batt for this reason.

Is there a way to make the BCDC charge both starting and house?

You could definitely figure out a way to do this, however I’m not sure it would be wise. A) you would lose the isolation by bridging them together and b) I’m not sure how well the OE electronics would respond to the almost 15V. My system shows 14.1 max on the starting side with usual charging around 13.7-13.9. Doubtful it would fry anything but something to consider.

One bit of trivia; most people say cars are 12V. They’re not. They’re 14V systems with a 12V nominal battery. At 12V resting charge your battery is around 50% discharged.

 

[mep1811]

I used a National Luna dual battery system. I also bought the Slee trays but switched the batteries. I made the P/S GP 35 battery the primary battery and the much larger GP 31 battery on the D/S my aux battery.

I've been very happy with the Battery Plus X2 Power batteries. Great warranty.

Slee Dual battery install

forum.ih8mud.com

 

[OregonLC]

Regarding alternators and charging, I found this interesting.

"Alternators are NOT chargers. Don't rely on your alternator to do the work of a charger. If your battery is discharged to the point where it cannot start your vehicle, use a charger as soon as possible to make sure your battery gets fully charged.

An alternator is meant to maintain a battery, not charge it."

From Optima. Though I believe the intent of this link is to steer someone toward the Optima brand chargers, I take it in its overall context of the purpose of an alt vs a deep cycle charging system.

 

[CharlieS]

Thanks for all of the great info. A lot of it is way over my head. I think I get the gist of it, but I'm a total novice.

At my rookie level, I like the posts that say something like "I have batteries xyz and abc and they fit the Slee tray and work well with the BCDC".

I'll do some more research based on the information you all shared. This gives me more leads to go on. I didn't even know about some of these brands prior to this thread (I've used Interstate batteries for many years because I thought they were good quality and there is a local distributor).

 

[Fisher23]

Regarding alternators and charging, I found this interesting.

"Alternators are NOT chargers. Don't rely on your alternator to do the work of a charger. If your battery is discharged to the point where it cannot start your vehicle, use a charger as soon as possible to make sure your battery gets fully charged.

An alternator is meant to maintain a battery, not charge it."

From Optima. Though I believe the intent of this link is to steer someone toward the Optima brand chargers, I take it in its overall context of the purpose of an alt vs a deep cycle charging system.

Just FYI: When batteries get down to zero volts the alternator will not charge the battery, and you need to use a battery charger to bring it back.

This is why aux batteries used for a Fridge or camp lights for example are best deep-cell or lithium and do need a charging system to bring them back from the dead (super low voltage situations).

That is what they are talking about there.

 

[TeCKis300]

Is there a way to make the BCDC charge both starting and house?

Yes, set them up as a single bank - KISS Dual Battery Upgrade

You'll have less complexity, more reserves, more current, and potentially that 150amp worth of charging speed direct from the alternator.

There are other ways to make sure you can always start the car: 1) put all accessories on a low voltage relay that detects when the batts are below a certain level and it disconnects the accessories 2) Separate lithium jump starter.

Other requirement is to use the batt chemistry the alternator charging profile is compatible with - flooded lead acid. They are dependable and long lasting when tendered by a matching charge profile. 5-7 years, just as every stock battery lasts.

 

[fireball]

Charlie, you should probably ask yourself if you really truly need a dual battery. If more folks started with this question, they'd realize the answer is NO, and avoid a lot of time, energy, expense, weight and complication in their system. I fell down the rabbit hole with my 100, and during 6 years of ownership, 70k miles of trips, overlanding, rock crawling and using it for its purpose, realized I would've been much better served with a group 31 main battery, a Noco jump pack, and portable solar panel.