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Can you get a secondary battery for the engine?

AccentedWanderer

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Can someone provide more insight on how the secondary battery would be charged?

I heard that the new 2021 F-150 stops charging battery when it reaches maximum amp hour that is preset in factory. If we add more batteries to it, it will never chage the new battery since the computer thinks the truck battery is already full because it does not know it now has two.
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Bocephus87

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Keep in mind, the goal of the battery in the hybrid system is primarily a brief temporary energy reserve. The goal isn't long-term storage, but rather to reapply the energy into the most beneficial work available. It's not intended to top off and deplete. It's duty is to collect waste energy and convert it back into kinetic energy. Be it to propel the truck or to energize the Inverter. Keep in mind the battery isn't charging over (estimated values pulled from nowhere) 70-80%% and likely wont deplete below 30-40%. This gives roughly an effective capacity of 40%.

I can see value in a larger battery to reduce engine cycling with the generator, but not sure the return on investment is there unless heavy use is anticipated. I plan on stress testing mine out in the sticks when I take delivery. Very glad to read others' experiences that have theirs already.
 

travisN000

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I installed a 40ah Lpf behind the seat. Removed the jack and auxiliary battery under rear passenger seat. The pos and neg leads just connected to the new battery. 5100 seeies fits nice. I have a powerboost with 7.2k. Deleted bms and I charge at 14.6v all the time.
Can you provide more info on the BMS delete? Did you just remove the current sensor under the seat from the negative wire, from the starter battery negative, or both? Do you recall what sort of charging voltage you were getting before removing/ disabling the BMS?

What do you use the battery for, and how is it holding up? Is it isolated from the starter battery when the truck is off? Any sort of low voltage / over-drain protection?

I've been using the stock accessory battery in my PB for running a 12v fridge throughout the summer and it seems to work well, but I was considering updating the battery to a 20+aH lithium so that I could use it to power a 12v heated blanket overnight for camping during the winter. My fridge has a low voltage cut off to protect the battery, but a heated blanket uses more power and does not provide battery protection.

I may just go with a 'solar generator', but it seems overkill as I don't need the AC inverter or solar charging functions; the upside of a portable battery pack is that the heated blanket / mattress pad could also keep the battery warm and better functioning in cold weather

Thanks!
 

astrand1

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I installed a 40ah Lpf behind the seat. Removed the jack and auxiliary battery under rear passenger seat. The pos and neg leads just connected to the new battery. 5100 seeies fits nice. I have a powerboost with 7.2k. Deleted bms and I charge at 14.6v all the time.

C14CDAF4-DF8A-40CA-82A0-BFD328136B53.png
Out of curiosity why? Is there a benefit to this?
 

Porpoise Hork

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Out of curiosity why? Is there a benefit to this?
Expensive way to prolong the time period for the truck entering Deep Sleep mode after being parked for an extended period of time would be my best guess.

Something you can also achieve by accessing the BCM module with Forscan and updating the 12v battery state of charge limit form OEM at 80% to 90-95%. This will bring the 12v charge limit up from 12.5 (80%) to 12.75-13.0v and prevents Deep Sleep for up to an additional week or two depending on ambient temps and battery age.

The PB already has a 35 or 70AH (can't remember the size) 7.5AH (thanks @Handle) deep cycle gel battery located under the rear passenger seat. This battery is linked through the BMS located at the primary 12v battery under the hood. This is a backup power source for the various modules in the event the primary battery were to fail. The lines form the aux battery to the primary/BMS module are not designed to carry high amp loads for starting only to supply backup power to the system when needed. Removing or circumventing them could possibly lead to issues as the electrical system in this truck is VERY complex and engineers spent a long time designing it to function a specific way. Altering that in many cases can/will cause problems.
 
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Handle

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Stock auxiliary battery is an AGM 7.5ah battery
 

Porpoise Hork

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Stock auxiliary battery is an AGM 7.5ah battery
Crap.. That's right. For whatever the odd ball reason (sleep deprivation from EOY IT scramble) I was thinking of the twin 35Ah gel batteries I have setup for my backup power on my saltwater fish tank and applied that to the PB reserve battery.

I need a vacation... 🤪
 

Handle

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It would be interesting to see how this battery mod has worked out for @Millionvill3 Beyond the crazy price my concern long term would be that you have connected a lithium battery in parallel with the AGM under the hood. Typically that’s not a great plan as their charging requirements are different. And yeah the auxiliary battery is isolated from the big AGM during the hi draw starting function but not when it comes to charging.
 

Porpoise Hork

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It would be interesting to see how this battery mod has worked out for @Millionvill3 Beyond the crazy price my concern long term would be that you have connected a lithium battery in parallel with the AGM under the hood. Typically that’s not a great plan as their charging requirements are different. And yeah the auxiliary battery is isolated from the big AGM during the hi draw starting function but not when it comes to charging.
Not sure, but you could always add a second 7.5AH like some of the non PB versions have. Another option is to see if a larger capacity sealed gel battery will fit under there instead.
 

travisN000

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It would be interesting to see how this battery mod has worked out for @Millionvill3 Beyond the crazy price my concern long term would be that you have connected a lithium battery in parallel with the AGM under the hood. Typically that’s not a great plan as their charging requirements are different. And yeah the auxiliary battery is isolated from the big AGM during the hi draw starting function but not when it comes to charging.

The charging requirements aren't that different for AGM and LiFePO4... both charge at about 14.5 volts; if the Li battery has a built in BMS as most do, it should protect itself from overcharge / over drain if needed.

The stock deep cycle AGM is 7.5Ah, but only half of that is usable without damaging the battery; replacing that with a similar sized 20-50Ah Li battery should give 4-10x more usable power before a recharge is needed, as Li batteries can handle near complete discharge without damage (and the BMS will protect it from over-discharge).
 

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Jbcaindo

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Good luck in a cold climate... Not very intelligent.

two oem 7.5ah aux batteries will physically fit in the under-rear-seat box. but if the bms is monitoring that aux battery AH as well, it'd be useless to upgrade without being able to modify the bms info
 
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SRHAGEN

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Not sure, but you could always add a second 7.5AH like some of the non PB versions have. Another option is to see if a larger capacity sealed gel battery will fit under there instead.
I think the issue is battery resistance. When altering a charging system battery resistance is important to know the charge rate required. Different battery technologies have diff characteristics. If you change the battery resistance you definitely have changed the current in the wiring and regulator of the charging system. Certainly why the FOMOCO chose to match the two batteries Ah requirement for convenience of one charging circuit. I’m sure there is some redundancy in the charging system, but a thorough understanding of it and the systems it supports, should be in hand before changing that secondary aux battery. For anything outside spec. Exspenive toy to experiment with. IMHO.
I’m sure there is away but the average diy r shouldn’t do it.
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