Adding a 2nd aux battery?

Vanguy · 05-31-2021, 08:31 AM

So I have a 2000 E150 with a factory option aux battery monted outboard of the frame rail on the passenger side. I also have another battery that is a deep cycle RV/Marine battery from Walmart. My question is could I possibly tie both batteries together in the same circuit but in different locations or would that be a bad idea? Trying to get a little extra capacity for an upcoming 2 night camping trip. I need to at least run my cpap and possibly a 12v cooler without spending a whole lot of money this time around.

I also have 2 100 watt solar panels that are mounted together on hinges. They stow in the box they were shipped in and unfold like a suitcase so I can put them anywhere the cables will let them reach.

My long term goal would be to prob do a diy lifepo4 bank or possibly adding another battery box next to the factory aux battery. I could fabricate 1 or 2 custom battery boxes to fit any size battery if needed. Just trying to put as little time and/or money into something that would just be replaced anyway.

Thanks...

86Scotty · 05-31-2021, 08:39 AM

what is the current second battery, just a FLA (flooded lead acid) old school type?

Generally, it is not advised to link two batteries that are not the same type and age in a system because the older or smaller one will negatively impact the newer/bigger. It all depends on how your chassis battery and this auxiliary battery are wired. Do you know if there is any kind of isolator between them already?

If they are simply linked by battery cables you could put an isolator between the chassis/frame battery (defined as one bank if only connected by cables) and your deep cycle RV/Marine battery creating a true 'house' battery. Physically, it would be simplest to do this from the current frame rail battery.

This isn't as simple as running cables but not difficult either. You need properly gauged wire and breakers along with an isolator.

posplayr · 05-31-2021, 09:02 AM

As stated Vanguy has a factory option aux battery at the frame. It would be straight forward to add a second box behind (sellers on eBay) the first with the same type battery in both boxes. Simply wire them in parallel. The isolation from the start battery is already there.
For small loads you could have one in the cab and one at the frame but that requires shout 10 ft of cable between. When you push current to the aux battery the one on a long cable away will never charge/ deliver current as well. this depends on cable size and would probable require a #6 awg 10 ft run to connect the batteries.

I added two factory boxes but not the factory relay and have wired them into a cabinet behind drivers seat using #6. So from where you are now buy the second box or build a supper box and keep both lead acid batteries out or the cab. The LiFePo4 is a whole other can of worms as I’m in process of doing that DIY as well.

The biggest I have found that will fit into the factory box is a group 24 deep cycle at Oreily that is 80 amp-he. Buy two fresh ones for $200.

Vanguy · 05-31-2021, 11:02 AM

Thanks posplayr. Sounds like my best bet for quick n dirty n cheap is to just put the 2nd battery I have in the cab and keep it seperate as a backup to the aux battery or run the cooler off of the aux battery that already has a standard 12v power plug wired to it and put the inverter for the cpap on the 2nd battery in the cab.

Good info on battery size as well. That works out actually since the 2nd battery is a 24DC. Not sure how many amp hr it is since it only has cranking amps listed on it. Guess it's designed for marine applications where it would be starting an outboard motor but also running a trolling motor, electronics, and possibly a live well pump with the engine off.

Vanguy · 05-31-2021, 12:30 PM

Posplayr I found a battery box on ebay without the lid for $20 plus shipping or $50 with the lid. Tempted to cheap out but maybe the lid is necessary or at least desirable? I COULD make something but time is a valuable commodity as well. Just mounting up something that's already fabbed and matching sounds like the ticket for this job.

posplayr · 05-31-2021, 12:58 PM

Quote:

Originally Posted by Vanguy

Posplayr I found a battery box on ebay without the lid for $20 plus shipping or $50 with the lid. Tempted to cheap out but maybe the lid is necessary or at least desirable? I COULD make something but time is a valuable commodity as well. Just mounting up something that's already fabbed and matching sounds like the ticket for this job.

I bought the complete boxes that had the tops and all the frame mounting hardware and the battery hold down inside.

I was planning on using this battery, even though it might be a little tall. The top is non-metallic and can be spaced up for clearance if needed. it is close.

https://www.oreillyauto.com/detail/c...250-super-duty

I don't know how much current you plan on pulling but I would also put one of these down into the first box to protect both. If you go with the O'riely 80- amp-hr that is 160 Amp-hr and at C/10 you have 16 amps.

A 300W inverter I have pulls 29 amps so it all depends on your setup. The 50 amp breaker will sustain 60+ amps for quite some time but will open before a 70 amp inline fuse (this is an estimate based on some recent tests).

As a benchmark using the breaker in series with the fusable link a 600 Watt invertor limited the draw to 50 amps. A 30 amp auto-reset breaker opened in 60 seconds and the 40A fusible link blew in 30 seconds. Based on this I'm sizing my LiFePO4 100 ampHr batts to 70 amps using 50 amp breaks and 70 amp fusible links. That is plenty of current for most anything you would probably do even for the pair of deep cycle batts.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Vanguy · 05-31-2021, 01:26 PM

This is my spare battery. I have yet to see what I have under the van already.

https://www.walmart.com/ip/EverStart...-MCA/180350522

posplayr · 05-31-2021, 05:09 PM

Quote:

Originally Posted by Vanguy

This is my spare battery. I have yet to see what I have under the van already.

https://www.walmart.com/ip/EverStart...-MCA/180350522

To fit the box (without alteration), I think the max length can be about 12 1/4" and the height needs to be right at 7" and no more than about 9" in the rear where the connector are. Teh to can be raised maybe 1 full inch (maybe) but tat 13" length is going to be a problem without cutting.

According to my notes:
the length is 12.25" from edge to edge of that turned it lip.
The width is 7.75"
The height is 7" in front and 8.75" in the rear (where the cables attach).

This O' Reilly deep cycle is 11 1/16" x 6 3/4" and 9 1/8" tall . So it fits but the lid needs to be spaced up about 1/2". Spacing up the lid (or just leaving it off) is much easier than going : LiFePO4 but this space constraints helped me make that decision

.

https://www.oreillyauto.com/detail/c...oaAoglEALw_wcB

Maybe just make a super box and you can fit a couple of the 100 AmpHr batteries. But hope you have a hydraulic motorcycle lift to let that thing down.

Vanguy · 05-31-2021, 05:56 PM

Yeah thought about the weight of 2 batteries and think 2 seperate boxes would be better. I could buy the cheaper box w/ no lid or prob just start from scratch. I have plenty of steel lying around to build one.

posplayr · 05-31-2021, 06:18 PM

Quote:

Originally Posted by Vanguy

Yeah thought about the weight of 2 batteries and think 2 seperate boxes would be better. I could buy the cheaper box w/ no lid or prob just start from scratch. I have plenty of steel lying around to build one.

The thought of combining my two factory boxes crossed my mind as well.

If I line up the 8 cells it will be much shorter than two battery boxes. Two boxes are redundant and the way I have been sizing everything I can run 1 as well as 2 albeit with less capacity.