triangles
Posts: 1139
Joined: Tue Aug 16, 2011 11:40 am
Location: Toledo, Ohio

Better 12V battery option?

Mon Nov 24, 2014 7:13 pm

I can't find any specifications for the 12V battery. It's model# is BTX 67R 390. It says 390 cold cranking amps on it. The "vehicle modifier" manual or whatever it's called says it's a standard automotive type battery. This would seem less than ideal since a standard automotive battery is engineered to provide a high current surge to start a gas engine. The engineering trade off for this is the battery has less overall capacity than it could and does not handle significant discharges well. It would seem a deep cycle battery would be more ideal for our car.
Does anyone have the specifications for the OEM 12V battery? I would specifically be interested in the capacity.
2014 Blue Candy FFE
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davideos
Posts: 409
Joined: Mon Jan 21, 2013 8:58 pm
Location: So Cal

Re: Better 12V battery option?

Mon Nov 24, 2014 8:07 pm

If you go with just a deep discharge, you're likely ok with any that will fit. I think a deep discharge is more geared for capacity rather than current. The biggest rate of discharge will likely be when the headlights are on, the climate control blower motor, the heated seats, and the radio blasting. An easy way could be to add up all the fuses for those devices and you will get a higher than needed current draw; but still likely within any deep cycle battery you are looking at. As long as you stick with lead-acid, you likely don't need to worry about the DC to DC charger since charging is regulated by voltage level alone...unlike other technologies.

My guess is that the Ford battery is a simple 36mo battery...cost reduced to meet the minimum requirements for an automotive battery. If you are thinking to get something different because the battery doesn't last very long, you'll likely be ok by simply buying a better high quality battery.

NightHawk
Posts: 535
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Location: Southern CA

Re: Better 12V battery option?

Mon Nov 24, 2014 10:24 pm

Are there any lithium-ion equivalents to replace the 12v lead-acid battery?
2014 Ford Focus Electric - Oxford White, Cloth Seats (Lease ended 9/28/2017)

Olagon
Posts: 169
Joined: Thu Oct 23, 2014 7:57 pm

Re: Better 12V battery option?

Mon Nov 24, 2014 10:41 pm

Good article here: http://www.plugincars.com/why-do-electr ... 29118.html

Anyone try one of these lithium alternatives?
- 2014 FFE Tuxedo with leather charged via home PV

Previous eco cars
- 2012 Mitsubishi iMiev
- 1995 Black Benz E300D running biodiesel
- 1995 Green Benz E300D running biodiesel

Next eco car
- Seven seat SUV all electric < $50,000

davideos
Posts: 409
Joined: Mon Jan 21, 2013 8:58 pm
Location: So Cal

Re: Better 12V battery option?

Mon Nov 24, 2014 11:21 pm

In some consumer Lithium rechargeable batteries, there are electronics that can shut the battery down when the level gets to a certain threshold that would otherwise cause harm to the battery. I would have to believe that an automotive lithium battery would have similar protection to protect itself from the alternator. The alternator was designed for use with lead-acid, not lithium. In the case of an FFE, the DC to DC converter was also designed for use with lead-acid. I do believe that a 12V lithium replacement automotive battery would likely work ok, but I would also have to believe there to be some added risk. With electrical components that separate the battery output to the car from the internal lithium storage, there are more possible points of failure. Also, as I mentioned, there may be circumstances that would case the battery to shut down due to the behavior of the DC to DC converter...or other condition. A lead-acid battery is just a dumb chemistry battery with no intelligence to screw things up.

I'd be curious if someone tries it, but for me, I think sticking with the lead-acid chemistry is the safest bet.

triangles
Posts: 1139
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Location: Toledo, Ohio

Re: Better 12V battery option?

Tue Nov 25, 2014 4:39 am

I had used a LiFePO4 battery pack in my motorcycle. The cost of the Lithium battery is slightly more but actually had less capacity than the lead battery. also below freezing temps the lithium battery all but shuts down. I would not use another lithium battery as a "starter" battery since it gets cold where I live. If I lived down south it might be a viable option.
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redcelt007
Posts: 25
Joined: Sat May 10, 2014 7:25 am
Location: Little Rock, Arkansas

Re: Better 12V battery option?

Tue Nov 25, 2014 7:18 am

According to the MotorCraft service manual, the battery is rated at 43 amp hours. Deep cycle batteries are usually rated in Amp hrs. I recently had to remove my 12V battery and tray to check a brake booster issue. Pretty light for a lead acid battery. Deep cycle batteries are much heavier due to their thicker plates. Might be tricky to find a deep cycle in the size and Ahr rating. Using a lithium battery would be risky, in my opinion, because of the charge is limited to 80-90% of full capacity. That dc-dc converter might not charge lithium properly.

hybridbear
Posts: 1425
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Location: Minneapolis

Re: Better 12V battery option?

Tue Nov 25, 2014 7:59 am

Some Fusion Hybrid/Energi owners have gone with an AGM deep cycle battery. The issue has been getting the new battery to fit. For those owners the deep cycle battery has fixed their low 12V battery issues.
2013 Ford Focus Electric - Ice Storm - leased through 8/15/16
Replaced by a 2016 Tesla Model S 60D

triangles
Posts: 1139
Joined: Tue Aug 16, 2011 11:40 am
Location: Toledo, Ohio

Re: Better 12V battery option?

Tue Nov 25, 2014 9:45 am

redcelt007 wrote:According to the MotorCraft service manual, the battery is rated at 43 amp hours.... Using a lithium battery would be risky, in my opinion, because of the charge is limited to 80-90% of full capacity. That dc-dc converter might not charge lithium properly.
Thanks for the info. Is there an actual manual other than the web based stuff? I'd like to get my hands on one.

I will probably buy a deep cycle AGM as hybridbear pointed out hybrid/energi owners have done.

At least the A123 based "12V" automotive batteries would be fine with the DC-DC charging. These packs are made by putting four cells in series and then adding addition cells in parallel to get usable capacity. You will often see them denoted as 4s2p, the number before the "s" indicates how many cells are in series and the number before "p" indicates how many cells are in parallel. So in the example I gave (4s2p) it would have 4 groups of 2 parallel cells in series for a total of 8 cells. The following specs are from memory while researching the feasibility f using a lithium pack in my motorcycle so I may be slightly off. A 4cell A123 based pack is nominally 13.2V. Each cell can safely handle up to 4v charging so as long as the DC-DC converter doesn't put out 16V+ (max converter output ~14.5V) it would be ok. Since the cell voltage never reaches 4v the battery is never charged to the theoretical 100% This video of me starting my motorcycle in cold weather demonstrates why lithium starter batteries (at least for ICE vehicles) have not caught on. Additional reasons not to use a pack like this is the potential for cells to not be balanced (all cells have same state of charge). It would take a complicated battery management system to keep things in balance. Also without battery protection circuitry, if you ever were to accidentally run the battery down, it would be destroyed and never hold a charge again. To build a 41.4Ah (each cell is 2.3Ah) pack for our car would be a 4s18p battery. That's 72cells! An 8 cell pack is about $100 so I imagine a 72 cell pack would be in the neighborhood of $900!!! Not a viable option!

I'm not nearly as knowledgeable about the larger higher capacity prismatic lithium cells, but I suppose it would be possible to make a 4 cell battery with them where you wouldn't really have to worry too much about the cells being balanced assuming they are balanced when the pack is assembled. From some quick googling for a 40Ah battery it would be 4x$120 cells = $480 just for the cells to build a "12v" battery! I don't know anyone who would spend that much instead of buying a cheap lead battery. It would cost even more to add protection from an accidental complete discharge. Additionally who knows if these cells can tolerate the 14.5V charging voltage from the DC-DC converter? It may be necessary to add a protection circuit for overcharging adding even more cost!

Edit:
I just saw another site that listed the 40Ah prismatic cells at about $50 which makes a 12v lithium pack more reasonable.
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redcelt007
Posts: 25
Joined: Sat May 10, 2014 7:25 am
Location: Little Rock, Arkansas

Re: Better 12V battery option?

Tue Nov 25, 2014 12:44 pm

Another thing to keep in mind regarding the dc-dc converter is that it can deliver as much as 100 amps of charge current to that 12 volt battery, according to the service manual. That's almost a 3C charge rate. I know of no other service manuals other than the online version. I paid for a year's subscription. It has really come in handy.

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