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First, you do not need a DC-DC charger with modern LiFePo4 batteries.

Second, do not buy batteries without external monitoring (Display or Bluetooth). It's a mystery to me why do people obsess with battle borns... they are at best mediocre and are way outdated technologically. Since the introduction of a common 100Ah drop in batteries (~5y ago) the capacity of LiFePo4 went up 3x and the price per Ah went 3x down.
Nowadays, any competent manufacturer should be able to offer 300Ah battery for ~$1000 and I don't see Battle Born updating their product line to reflect that.

Third, battery isolator is a bad idea for LiFePo4 batteries. They are designed for LeadAcid batteries and will unpredictability affect charging due to low resistance of lithium batteries. Just use a quality fuse-breaker instead.

Yes, DC-DC is a nice piece of equipment and it might be a safer option if your battery is "dumb" or/and you lack the basic understanding of how the charging works. But you won't find a DC-DC charger capable of using the full potential of PM alternator charging of 75A and they are expensive. Nowadays, you can get 100Ah LiFePo4 battery for the price of a good DC-DC charger.

Also, if you are willing to tinker, you can build a ~300Ah battery for under $800. And it will have the same dimensions as a single classic 100Ah like battle born.
 

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Thanks for that @Kip-on-truckin

I charge direct from the PM 180amp alternator about 95% of the time to replenish my 250ahr Rolls AGMs.

My understanding is the PM Computer controls the PM Alternator's "Regulator".

Correct! In the old days, a mechanical device called a voltage regulator would tell the alternator to charge. These days, the main engine ECU does that.
 
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Correct! In the old days, a mechanical device called a voltage regulator would tell the alternator to charge. These days, the main engine ECU does that.
 
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Carry a spare alternator???
To me, as one who knows almost nothing about vehicles i may as well tow a spare van 😂 I wouldn't even know how to locate the alternator.

As for lithium vs old tech, I just bought lithium cuz I want easy. I don't understand any battery tech so easy is worth a lot for me. Plus a lot smaller and lighter, last longer and no fuss. Even lithium batteries are big af. That one was one of the only decisions I didn't have to ponder for long.
Sooo, I dont understand how anyone would come to think of Li as "easy" compared to lead acid? Yes, there are more youtube videos describing battleborn battery installs in vans but that is just because they are really good at marketing. There is waaaay more complexity with any Li battery system in camper van compared to lead acid. With Li the temperature operation range is way narrower. They need a BMS (which sometimes fail). You need to charge them with a B2B, etc, etc. With a sealed lead acid/agm battery you can literally charge it from the alternator with a $20 solenoid and get the full output of the alternator for fast charging as I do. That doesn't mean that Li isnt the best choice for some users, depending on their needs/overall design considerations, but I certainly wouldn't classify it as the "easy" option.

Im not going to carry a spare alternator but great to know that they are cheap and fairly easy to replace. People here often bring up this concern that a camper battery could overtax the alternator but as far as I know noone has actually reported alternator failing from charging 2nd battery.
 

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Sooo, I dont understand how anyone would come to think of Li as "easy" compared to lead acid? Yes, there are more youtube videos describing battleborn battery installs in vans but that is just because they are really good at marketing. There is waaaay more complexity with any Li battery system in camper van compared to lead acid. With Li the temperature operation range is way narrower. They need a BMS (which sometimes fail). You need to charge them with a B2B, etc, etc. With a sealed lead acid/agm battery you can literally charge it from the alternator with a $20 solenoid and get the full output of the alternator for fast charging as I do. That doesn't mean that Li isnt the best choice for some users, depending on their needs/overall design considerations, but I certainly wouldn't classify it as the "easy" option.

Im not going to carry a spare alternator but great to know that they are cheap and fairly easy to replace. People here often bring up this concern that a camper battery could overtax the alternator but as far as I know noone has actually reported alternator failing from charging 2nd battery.
Maybe more complicated but easier for a newb like me to install and use, and maintenance free.

I read lots of posts on here about how lithium isn't easier, usually followed by an explanation that I can't understand (often from people who already have experience with older batteries, and already have the knowledge needed). With lithium, I can let the pros figure out how to maintain it and charge it, buy the product, plug and play.

Everything I own uses lithium batteries except cars.
 

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Sooo, I dont understand how anyone would come to think of Li as "easy" compared to lead acid? Yes, there are more youtube videos describing battleborn battery installs in vans but that is just because they are really good at marketing. There is waaaay more complexity with any Li battery system in camper van compared to lead acid. With Li the temperature operation range is way narrower. They need a BMS (which sometimes fail). You need to charge them with a B2B, etc, etc. With a sealed lead acid/agm battery you can literally charge it from the alternator with a $20 solenoid and get the full output of the alternator for fast charging as I do. That doesn't mean that Li isnt the best choice for some users, depending on their needs/overall design considerations, but I certainly wouldn't classify it as the "easy" option..
Probably because it sounds like you do not fully understand LiFePO4 batteries. Flooded, AGM and Gel batteries all need a proper 3 stage charge to ensure an expected lifespan. They also all need to be fully charged often. LiFePO4 batteries DO NOT need 3 stage charging and they do not have to be fully charged. LiFePO4 batteries in a Promaster do not need a B2B charger. Flooded, AGM and Gel do (or rather should). In a Promaster you can literally just install an on/off switch from the positive post of the chassis battery and the positive post of the LiFePO4 battery and the alternator will charge it properly with no issues. Today’s popular LiFePO4 batteries like Battleborn have a built in BMS and a long warranty so you don’t have to worry about anything. They all also now have built in heating so you no longer have to worry about low temperature charging.
 

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In a Promaster you can literally just install an on/off switch from the positive post of the chassis battery and the positive post of the LiFePO4 battery and the alternator will charge it properly with no issues.
if that's the case how do you size that wire? 1 battery or a 4 battery bank?
 

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Jostalli, from what I’ve seen coming from the alternator, I don’t see how you could not be correct. Nice level voltage just what BB recommends. Yet BB tells me I would have to install a B2B?

I am being sorely tempted to risk indigestion from eating all the bad things I’ve said about lithium over the years and make the jump (not necessarily to BB). My persistent problem with AGM is that 90% of our usage puts us in the absorption phase when we charge (~40Ah on 200Ah batteries), so no matter how many electrons are available, complete recharge may not even happen over the course of a day.
 

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Probably because it sounds like you do not fully understand LiFePO4 batteries. Flooded, AGM and Gel batteries all need a proper 3 stage charge to ensure an expected lifespan. They also all need to be fully charged often. LiFePO4 batteries DO NOT need 3 stage charging and they do not have to be fully charged. LiFePO4 batteries in a Promaster do not need a B2B charger. Flooded, AGM and Gel do (or rather should). In a Promaster you can literally just install an on/off switch from the positive post of the chassis battery and the positive post of the LiFePO4 battery and the alternator will charge it properly with no issues. Today’s popular LiFePO4 batteries like Battleborn have a built in BMS and a long warranty so you don’t have to worry about anything. They all also now have built in heating so you no longer have to worry about low temperature charging.
I admit that I am not a battery know-it-all and am learning so I have a few questions if you dont mind:

Is'nt the PM alternator system designed to charge the starter battery (sealed lead acid I believe)? If its designed to charge the starter battery and I use the same chemistry for my camper battery why do I need a B2B?

If LiFEPO4 batteries dont require a B2B why does everyone use one?

Regarding the battery heating, lets say I live in Colorado (i do), for 7 months out of the year nightime temps drop below 32f. The battery has to warm itself before it can charge, so on short trips its not going to charge. I use the van a lot for skiing and I rely on 30-45 minutes of driving after a ski day to provide enough bulk charge to power the van for another 12 hours or so (charging at 50ish amps to AGM). If that first 30-45 minutes of driving and alternator output were used to warm the batteries instead of charge them I would run out of power. Admittedly this may be a fairly specialized use case but doesn't seem like "I no longer have to worry about low temp charging". Also that battery with the built in heater costs even more.

I know AGM optimal charge profile is slightly different than what the van alternator outputs but is'nt LiFEPO4 charge profile also slightly different than what the van alternator outputs?

Have read instances of BMS' failing and rendering expensive Li batteries useless. Battleborn does have a 10 year warranty but its got a whole page of exclusions.
 

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Maybe more complicated but easier for a newb like me to install and use, and maintenance free.

I read lots of posts on here about how lithium isn't easier, usually followed by an explanation that I can't understand (often from people who already have experience with older batteries, and already have the knowledge needed). With lithium, I can let the pros figure out how to maintain it and charge it, buy the product, plug and play.

Everything I own uses lithium batteries except cars.
The only Lead acid batteries that require "maintence" are flooded lead acid (the ones with caps on the tops). AGM, sealed lead acid, gel, etc are all just as maintence free as the Li batteries and there are fewer components (bms, heaters, lots of internal wiring, etc) to fail.

Li batteries are the obvious/only choice for low capacity portable consumer electronics used primarily indoors (computers, phones, etc).

Consider that the prius prime plug in hybrid has a 12v sealed lead acid battery in addition to its large Li traction battery. There is still a use case for both lead acid and Li batteries. Some van camper conversions are better off with lead acid, some better off with Li, its still nuanced which is why all the convo here and elsewhere about what batteries to use when, how to charge, etc, etc...
 

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if that's the case how do you size that wire? 1 battery or a 4 battery bank?
There are many variables but assuming you have a large LiFePO4 battery consisting of multiple batteries you would size the wire according to the max output of the alternator. Since we know the max output of the Promaster alternator does not exceed 150 amps you could size according to that.
 

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Jostalli, from what I’ve seen coming from the alternator, I don’t see how you could not be correct. Nice level voltage just what BB recommends. Yet BB tells me I would have to install a B2B?

I am being sorely tempted to risk indigestion from eating all the bad things I’ve said about lithium over the years and make the jump (not necessarily to BB). My persistent problem with AGM is that 90% of our usage puts us in the absorption phase when we charge (~40Ah on 200Ah batteries), so no matter how many electrons are available, complete recharge may not even happen over the course of a day.
Battleborn and others always recommend a B2B charger because it is the safest, most controlled method of alternator charging (with the exception of a Victron Buck Boost). It is also universally accepted across any vehicle. When we build in the new Sprinters we must use a B2B charger or a Victron Buck Boost because it has a “smart” alternator or variable voltage alternator. Promasters have been known to deliver a consistent 13.8V-14V from the alternator, which is perfect for LiFePO4 batteries. The only issue would be if your battery is having a balancing issue and you are only using alternator charging as your charge source. You would never get to the battery‘s set voltage to initiate cell balancing. Normally that is at around 14.2V. We address this by setting our absorption voltage on our solar charge controller to 14.2V.
 

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I admit that I am not a battery know-it-all and am learning so I have a few questions if you dont mind:

Is'nt the PM alternator system designed to charge the starter battery (sealed lead acid I believe)? If its designed to charge the starter battery and I use the same chemistry for my camper battery why do I need a B2B? You need a B2B with flooded, AGM and Gel because those batteries need a proper 3 stage charge. Your alternator is not a 3 stage charger.

If LiFEPO4 batteries dont require a B2B why does everyone use one? Because they are the safest, most controlled charge option from a vehicle alternator (with the exception of a Victron Buck Boost). They are also universally accepted across all vehicles. Vehicles with “smart” alternators like the new Sprinters absolutely need a B2B because their voltages are bouncing up and down as you drive.

Regarding the battery heating, lets say I live in Colorado (i do), for 7 months out of the year nightime temps drop below 32f. The battery has to warm itself before it can charge, so on short trips its not going to charge. I use the van a lot for skiing and I rely on 30-45 minutes of driving after a ski day to provide enough bulk charge to power the van for another 12 hours or so (charging at 50ish amps to AGM). If that first 30-45 minutes of driving and alternator output were used to warm the batteries instead of charge them I would run out of power. Admittedly this may be a fairly specialized use case but doesn't seem like "I no longer have to worry about low temp charging". Also that battery with the built in heater costs even more. When you are using your van this is a non-issue because there is typically a constant discharge on the battery, thereby keeping it warm. You are also most likely keeping your petrol heater on. If you have solar you will have the panels powering the heating strips in the batteries. Battleborn actually has a manual heating pad switch to keep them heated.

I know AGM optimal charge profile is slightly different than what the van alternator outputs but is'nt LiFEPO4 charge profile also slightly different than what the van alternator outputs? No. When we say charge profile we are referring to stages like bulk, absorption and float. Your AGM needs a 3 stage. LiFePO4 only needs 1 stage (bulk).

Have read instances of BMS' failing and rendering expensive Li batteries useless. Battleborn does have a 10 year warranty but its got a whole page of exclusions. Battleborn batteries as well as others like Relion have few stories of failures anymore. You can really push them and they keep delivering.
 

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I keep hearing about people keeping the heat on in their vans 24x7 to keep the batteries warm. Maybe that is where I am going astray. I only run the heater when Im in the van since its freezeproof.

It sounds like you're saying I would want to upgrade my AGM with heated battleborns and run my heater 24x7 and get a B2B. That will be how many thousand dollars? No thanks, im on year 4 of charging AGM via alternator, 4 season use, no issues. To each their own! Id rather buy another 1kwh Li ebike battery.
 

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I keep hearing about people keeping the heat on in their vans 24x7 to keep the batteries warm. Maybe that is where I am going astray. I only run the heater when Im in the van since its freezeproof.

It sounds like you're saying I would want to upgrade my AGM with heated battleborns and run my heater 24x7 and get a B2B. That will be how many thousand dollars? No thanks, im on year 4 of charging AGM via alternator, 4 season use, no issues. To each their own! Id rather buy another 1kwh Li ebike battery.
I’m not saying to keep your heater on just to keep your batteries warm. I was addressing your Colorado skiing scenario. If you are using the van then you will have a constant load on the batteries, thereby keeping them above freezing. You may also have solar providing chargjng while you are away. Chances are you will also have your heater on so you arrive back to a warm van after skiing.

I am definitely not telling you to upgrade your AGM for lithium if you are happy with what you have.
 

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I’m not saying to keep your heater on just to keep your batteries warm. I was addressing your Colorado skiing scenario. If you are using the van then you will have a constant load on the batteries, thereby keeping them above freezing. You may also have solar providing chargjng while you are away. Chances are you will also have your heater on so you arrive back to a warm van after skiing.

I am definitely not telling you to upgrade your AGM for lithium if you are happy with what you have.
I dont keep the heat on when I leave the van for more than a hour or so since my propex heater only takes about 10 min to warm the van from freezing to a comfortable temperature. My 7 gallon water tank takes a very long time to freeze.

I am happy with what I have and it works almost perfectly for my use case and costs a small fraction of a Li system and is maintence free and was easy to install. Everyone should know that they do not have to spend thousands on Li batteries to enjoy their camper van. Not that there's anything wrong with spending thousands on batteries.

I still dont understand why the starter battery gets by just fine with single stage charging from the alternator but a camper battery of the same chemistry needs a b2b with 3 stage charging?
 

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I am installing a Victron Orion-Tr DC DC converter. Easy to do and no concerns with Lithium battery monitoring and I can monitor through bluetooth on the app
 

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Yeah, I've seen some of those combined units. While I'm a big fan of "stacking" functions, it does make me a little nervous to depend on a single component for multiple functions . . .
We often 're-hear' the argument that one shouldn't use a combo unit because you don't want to 'put all your eggs into one basket'. Maybe it's our 'single engine' private pilot heritage that makes us smile a bit at this argument. Years and thousands of hours ago we had to confront the likelihood of engine failure and its corresponding consequences and concluded that the chances of the former were insignificant enough that we could accept the risk of the latter. If an internal combustion engine (with its hundreds of very quickly moving and reciprocating parts) can be made reliable enough to place our lives upon it, surely a modern electronic device with only a fan and on/off switch as its moving parts can be relied upon. And if it does fail, well, you're already on the ground.

Seriously, though . . . the 'smoothness' of combo units should not be ignored. Yank the shore power plug and inside the ProMaster the transition from shore to inverter power is so seamless that the lights don't even flicker. Computers (even those without batteries) continue uninterrupted as if connected to a UPS (uninterruptable power supply). All 120VAC outlets are treated the same. They are either connected to shore power or to inverter power. And then there's the issue of neutral bonding/grounding (where the neutral must be connected to ground/chassis when operating on inverter power and disconnected from ground/chassis when supplied by shore power) - - just another of the functions that combo units do 'for you'.

Settle those nerves - - go combo!
 

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I still dont understand why the starter battery gets by just fine with single stage charging from the alternator but a camper battery of the same chemistry needs a b2b with 3 stage charging?
The simple answer is: Starter batteries never get charged. Your starter battery is fully charged when you drive off the show-room floor and never gets discharged (unless, in the old days, you left you lights on!). From the moment your turn the ignition on, your alternator is maintaining your already fully charged starter battery at full charge. Ignition off - - the battery just sits there at full charge waiting for you to re-ignite the engine and turn the alternator back on.
 

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The simple answer is: Starter batteries never get charged. Your starter battery is fully charged when you drive off the show-room floor and never gets discharged (unless, in the old days, you left you lights on!). From the moment your turn the ignition on, your alternator is maintaining your already fully charged starter battery at full charge. Ignition off - - the battery just sits there at full charge waiting for you to re-ignite the engine and turn the alternator back on.
Implausible but that's the only explanation ive heard. Most of us probably run the radio on our PMs while parked all the time. When I was doing a lot of work on my conversion I didnt drive the van for weeks but used the radio and lights lots. The battery is 4 years old and is not showing any signs of needing to be replaced yet. If the starter battery was only designed to start the vehicle it would have very low capacity, less than 5ah would be plenty. Why are they using such a large batteries (100ish ah) for the starter battery if it's not designed to be discharged and recharged?

@jostalli said "Flooded, AGM and Gel batteries all need a proper 3 stage charge to ensure an expected lifespan. They also all need to be fully charged often."
How have boats and RVs relied on single stage alternator charging alone for accessory/camper battery charging for so long (75+ years) without major issues?
 
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