secondary battery question

[modeler]

I am looking for a LIFEPO battery 100AH, mostly charged at home, and stay charged/re-charge in car while on road/camping trip.

I only need LIFEPO battery to maintain camper light/fridge small things at 12v, but not helping engine starter battery.

So instead of big dual batt system with 100A wire and battery isolator, can I simply use only DC-DC charger to charge at about 10amp only to second LIFEPO battery while car is on?
Right now I have already had 25AMP circuit to power trailer lighting module, I probably can spare another 10amp to maintain the second battery, so I don't need to update existing wiring. All I need is splice another hot wire from the 25AH hot to DC charger to charge the second battery.
Also I only want battery to be there in roadtrip season, so figure do a portable installation.

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[GATORB8]

This is a trailer camper? Any specific reason you want it in car?

 

[modeler]

This is a trailer camper? Any specific reason you want it in car?

tent trailer,
Road trip, want fridge stay in car
Camp in bear country, want to lock food in car.

By the end is same question, can I just using charger to charge, instead of a big wire installation

 

[GATORB8]

tent trailer,
Road trip, want fridge stay in car
Camp in bear country, want to lock food in car.

By the end is same question, can I just using charger to charge, instead of a big wire installation

Yes you can just use a DC-DC charger and a Lifepo. The reason I ask is Portable Power Stations have come down in price and may be a better form factor for what you are looking for, and will have on board DC-DC and AC chargeing, and on board 12V and inverter output.

 

[YBABRAT]

This can charge without need of a LifePo4 charger. Tested on Dodge Challenger and Charger electrical system as a drop in.

https://antigravitybatteries.com/products/starter-batteries/automotive/ag-h7-rs/

 

[OminousSkitter]

This can charge without need of a LifePo4 charger. Tested on Dodge Challenger and Charger electrical system as a drop in.

https://antigravitybatteries.com/products/starter-batteries/automotive/ag-h7-rs/

NEW! Lightweight Lithium Batteries with Wireless Remote Built-In Jump Starting!

I love the new wireless jump starting batteries. Fantastic technology, rivals Tesla (person, not car).

 

[YBABRAT]

I love the new wireless jump starting batteries. Fantastic technology, rivals Tesla (person, not car).

I plan on getting one. Too many things on my plate. An EVO VR10, all season tires for 18x10 rims, and a few overtime pay checks. Ha!

 

[GATORB8]

This can charge without need of a LifePo4 charger. Tested on Dodge Challenger and Charger electrical system as a drop in.

https://antigravitybatteries.com/products/starter-batteries/automotive/ag-h7-rs/

Well, it’s built into the battery, but you are talking significant money for the starting capability that is not needed in this use case. 80 ah for $1300 compared to 100 ah for ~$300 and $100 for a DC-DC charger.

 

[YBABRAT]

Well, it’s built into the battery, but you are talking significant money for the starting capability that is not needed in this use case. 80 ah for $1300 compared to 100 ah for ~$300 and $100 for a DC-DC charger.

I wanted a drop in that doesn't need any changes to operate. The lower 80Ah rating is for the jump start reserve.

 

[GATORB8]

I wanted a drop in that doesn't need any changes to operate. The lower 80Ah rating is for the jump start reserve.

That’s the battery capacity. I’m not saying it’s bad, just not really suited for this purpose (auxiliary house battery).

 

[AndySpill]

Do be aware of the LiFePO4 battery charging limitations in below freezing temperatures should your Canadian domain find you experiencing such cold conditions in your outtings.

I do imagine, since you''' be limiting main charging to home, and top of charging to times when the engine is running, that for the latter, cabin temperature can be controlled.

 

[Reinen]

I am looking for a LIFEPO battery 100AH, mostly charged at home, and stay charged/re-charge in car while on road/camping trip.

I only need LIFEPO battery to maintain camper light/fridge small things at 12v, but not helping engine starter battery.

So instead of big dual batt system with 100A wire and battery isolator, can I simply use only DC-DC charger to charge at about 10amp only to second LIFEPO battery while car is on?

Yes. The Dual Battery approach is a bit old school at this point. A DC-to-DC charger going to an isolated LiFePO4 battery is a good modern option that will never drain your starter battery. You just need to make sure the DC-to-DC charger only gets power when the engine is running, otherwise you defeat the purpose.

Right now I have already had 25AMP circuit to power trailer lighting module, I probably can spare another 10amp to maintain the second battery, so I don't need to update existing wiring. All I need is splice another hot wire from the 25AH hot to DC charger to charge the second battery.

If the combined amperage of the trailer lighting, fridge, etc does not exceed the capacity of the wire then this is an option. However a 10A DC-to-DC charger will only increase a 100AH battery by 10%/hr taking 10 hours of engine run time to fully charge. It seems the DC-to-DC charger might be a bit underpowered or a 100AH battery is a bit over sized. It will work but it will be really slow to charge.

I have a 100AH LiFePO4 battery paired with a 50A DC-to-DC charger so I can have 24 hrs of fridge & accessories with only 2 hours of driving.

Also I only want battery to be there in roadtrip season, so figure do a portable installation.

If you're going to do a portable installation then it may make more sense to get a portable lithium power bank. By the time you add up all the parts and effort of the DIY system you'd be building they start to become comparable. The portable power bank will be much easier and provide more options.

 

[GATORB8]

If the combined amperage of the trailer lighting, fridge, etc does not exceed the capacity of the wire then this is an option. However a 10A DC-to-DC charger will only increase a 100AH battery by 10%/hr taking 10 hours of engine run time to fully charge. It seems the DC-to-DC charger might be a bit underpowered or a 100AH battery is a bit over sized. It will work but it will be really slow to charge.

Thinking a little more about this.

OP, do you have a house battery on the trailer? If not, you are drawing down your starting battery with the alternator off when using the lighting in the trailer.

What that also means is that your two circuits would not be used at the same time (Lifepo charging and lighting), so there is no reason to run the second circuit unless you are upsizing the charger like Reinen suggested. You could use the 25 amp circuit for the charger.

Note, if it's the battery charger circuit in the OEM trailer connector, it appears to be 30 amp fused, which should allow you to run a 20+ amp DC-DC charger.

Touching on batteries if you decided to not go with a portable packaged system. You could consider a 50 AH or a mini 100 AH (check out LiTime's offering there). I run 3 x 100 AH batteries in the trailer and it takes up a lot of space.

 

[Wrangler man]

I am looking for a LIFEPO battery 100AH, mostly charged at home, and stay charged/re-charge in car while on road/camping trip.

I only need LIFEPO battery to maintain camper light/fridge small things at 12v, but not helping engine starter battery.

So instead of big dual batt system with 100A wire and battery isolator, can I simply use only DC-DC charger to charge at about 10amp only to second LIFEPO battery while car is on?
Right now I have already had 25AMP circuit to power trailer lighting module, I probably can spare another 10amp to maintain the second battery, so I don't need to update existing wiring. All I need is splice another hot wire from the 25AH hot to DC charger to charge the second battery.
Also I only want battery to be there in roadtrip season, so figure do a portable installation.

Been using these products for a long time. In trying various configuration over the years without much luck. This setup worked flawlessly on a 2 week 4,000 MI Overland trip across the Great West recently.

 

[smokeythecat]

Camp in bear country, want to lock food in car.

That's probably not a good idea.

https://www.cbc.ca/news/canada/british-columbia/bear-car-protein-bars-1.3647881

This happens on a regular basis in Yosemite as well.

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