# Auto Battery Replacement with Li?



## McRat (Jul 10, 2012)

Anyone running LiFePO4 (4s) as a replacement for their ICE car battery?

Some battery MFR's are claiming it's a drop-in replacement using the factory charging system, and have a 3 year life.

Not sure I believe them.


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## Ziggythewiz (May 16, 2010)

What's not to believe? A bit of a BMS to prevent overcharging and you'd be good to go. You'd need some insulation for extremely cold environments.


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## McRat (Jul 10, 2012)

I seldom take mfr claims at face value by themselves. 

They tell you the best results, and "forget" to mention any downsides.

According to the MFR, you do not need anything like a BMS. You take 4 cells in series, and just put posts on them. There is no circuitry in the them that they mention. 

I guess I going to clamp these A123 cells together and test it on a forklift and use a infrared thermometer. Then put them in a front battery car, then a rear battery car, and finally in a diesel. I want to play with Li batteries before I buy and destroy a $10,000 array of them.


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## Ziggythewiz (May 16, 2010)

Yeah, it's not that simple. In an EV it would be very easy because you control everything in and out, but as a drop-in for OEM you'd have to have protection for both overcharge and overdischarge. 

How often do people leave their headlights on? A lead battery would come back from that a number of times, and cost $50-100 to replace. A handful of lithium cells would likely not come back, and cost at least 2-4 times that.

Done right, however, it should last much more than 3 years, likely over 10.


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## McRat (Jul 10, 2012)

Ziggythewiz said:


> Yeah, it's not that simple. In an EV it would be very easy because you control everything in and out, but as a drop-in for OEM you'd have to have protection for both overcharge and overdischarge.
> 
> How often do people leave their headlights on? A lead battery would come back from that a number of times, and cost $50-100 to replace. A handful of lithium cells would likely not come back, and cost at least 2-4 times that.
> 
> Done right, however, it should last much more than 3 years, likely over 10.


Over discharge! The factory alternator on a car is ~13.8-14.1v IIRC, and it's constant drain when operating. But, if your stereo in the OFF position uses power (they do) or security system, then you could certainly hose the battery.

So adding some kind of circuit that disconnects the battery when it falls below 2.7v per cell would be smart? I guess that's where a BMS comes in?


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## dtbaker (Jan 5, 2008)

McRat said:


> Anyone running LiFePO4 (4s) as a replacement for their ICE car battery?


in a race application it would save some weight..... but would certainly not be kind to the Li cells with the high-C draw required for the ICE starter motor. They might survive for a reasonable time since the duration of high C draw is short while starting the car; but would certainly be catastrophic if lights were left on and drained to 0.

If carefully top-balanced initially, 4 cells *should* stay in balance and not be damaged by the alternator if the charge control is typical 13.8-14.0 volts


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## Ziggythewiz (May 16, 2010)

I don't understand the difference, but cranking amps are measured much differently from the standard amp draw we're familiar with. On my load tester 50A = 500 CCA IIRC


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## Daox (Jan 18, 2008)

I am seriously thinking about trying out a very small A123 (4S) pack in my 97 Toyota Paseo (not an EV, just normal gasser). I plan on picking up a few cells this weekend at Drive Green Expo in Madison, WI. After I tinker with them they'll likely go into the car.

Overcharging shouldn't be a problem since the alternator puts out ~13.5V (3.375V/cell). At that voltage the cells should stay around 50% SOC constantly. So, you don't have nearly the full capacity of the cells, but its only for starting the car so it pulls 200A (I've measured it) for a split second and quickly drops off. This should be no problem for the A123 cells. My only slight concern is when winter rolls around what'll happen.

Overdischarging is a problem, but its a problem with any battery you have in there. Just don't leave stuff on. The price of 4 A123 cells really isn't a ton more than a normal battery. In fact I think I've paid more for an optima starting battery in the past.


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## MN Driver (Sep 29, 2009)

I've seen a Youtube video of people trying to start a car in Europe with Headway cells. I think it was a Swedish video or something I don't know my languages though. The video details were in choppy English but it said that it was the coldest day of the winter at night and the car was parked outside the whole night. It wouldn't turn the engine over right away so he cranked it for 5-10 seconds at a time and let it rest for about 20 seconds and each time he tried it heated up the battery internally(he kept putting his hand on it and commenting about it) and the cranking performance actually increased until the car could start. I'd imagine some insulation would help during the winter months, especially if you need to use this technique since these cells have plenty of external surface area and might lose the heat that would be gained while trying to crank the engine.

...then again for A123 cells, this might not be an issue but remember that if the car takes 200 amps to start in the summer, it's going to take more current in the winter when the oil is thicker. Remember though that CCA is a rating of how much amperage a battery can provide while cranking at 0f(-18c) for 30 seconds without dropping to 7.2 volts. So if the A123 cells can beat the cars CCA rating without dropping below 1.8vpc on the coldest night, you're set. You could always test this, put the 4 cells in a freezer with the temperature to the fridge and freezer set to their coldest for a day with a thermometer in the freezer next to the cells. If you can get them cold enough, use an automotive load tester and see what voltage sag you get at 400 amps or whatever the CCA rating is. Since the performance will improve with cranking due to the internal heating, your test would only need to be 5 seconds or whatever your load tester is rated for. I think mine is rated for 15 seconds, but if I set it on top of a box fan I could probably stretch it to 30 seconds. I think I got mine for $40 using a 20% coupon at Harbor Freight when they were on sale. It's the big 500 amp one with the knob that allows you to adjust current. Another thread someone says you can test a single cell with it at 300 amps if you get enough air through it. Cheap cell tester, just not an automated load but good enough for me, not sure why people are spending gobs of money on expensive equipment to test their cells when they could just get a good DC clamp on and adjust the load to a constant amperage and use a stopwatch. Maybe I'm just old fashioned but 300 amp constant load or buy two and you've got 600 amps for $100 is a better deal than the gobs of money people spend to do one time tests of the cells they want to use. My hobby charger that I have would chart the results, I think I spent $50 for mine but I bought it for cycling NiMh cells, but there are cheaper ones.


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## Ziggythewiz (May 16, 2010)

Meh...noobs think a 20% off HF coupon is good...40-60% is where it's at


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## Forse (Dec 21, 2009)

I've used a 4S1P A123 2,3 a/h bettery in my two bikes the last few years. I've had no problems even though the bikes charge to 14,4 v.

A 4S2P battery started my car, ford mondeo 2.0 gas. but couldn't provide power after more than a days standstill.

No BMS, don't belive it is nessesary.


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