I started this thread because of a discussion here:
https://www.fiatforum.com/500/455287-battery-specs-3.html
It started with a "supercapacitor" comment.

My opinion is that LiFePO4 is not a viable "drop-in" replacement for lead acid in a modern car. Super capacitors on their own are a complete non starter. The only advantages of LiFePO4 are lighter weight, higher discharge currents and possible longer life. Proponents say you can use a battery of 1/4 to 1/10 the AH rating of the lead acid. I disagree mainly because they will not support the modern electrical systems when the engine is not running. Threr are several disadvantages, can't chrge below 0 Deg C, may need special chargers / battery management, can de distryed by discharging below ~8V.
Some links from both sides:
http://www.lithiummoto.com/faq.html
https://electronics.stackexchange.com/questions/137249/using-lifepo4-battery-as-car-battery
ttps://www.physicsforums.com/threads/replacing-a-lead-acid-12-volt-battery-with-a-lithium-ion-polymer-battery.294828/
http://www.diyelectriccar.com/forum...tions/221531/supercapacitors-as-car-batteries

Robert G8RPI

Fiat lost to LiFePO4 fire

http://www.batteryvehiclesociety.org.uk/bvsorguk/forums/viewtopic.php?t=1825

Robert G8RPI.

g8rpi said:

Proponents say you can use a battery of 1/4 to 1/10 the AH rating of the lead acid.

Click to expand...

The rule of thumb is 1/3rd. I use a little less but I've backed it up with a supercap. My Fiat ran just fine on just 7.2Ah, no super cap. How much head room you want is up to you.

I disagree mainly because they will not support the modern electrical systems when the engine is not running.

Click to expand...

It's the exact opposite in fact. A 12v 60+Ah battery immediately drops to 12v when you turn off the engine (and have say the A/C and radio on). The 14.4Ah LiFe holds close to 13v, and I'd struggle to ever get it as low as 12v.

Pb batteries need regular maintenance. With the 60Ah battery I'd connect the 7.2A charger for a couple of hours every week or so. The LiFe needs nothing. Connecting the charger goes straight into maintenance mode.

Even if they had the same self discharge rate, 5% of 60Ah is a lot more than 5% of 14.4Ah. In practice, the depletion rated of a LiFe is more like 1%. I've got unassigned batteries that have sat for years and still hold a charge. You'd have to have a very poor BMS to be losing 5% in a LiFe.

The extra voltage and reduced alternator load have improved engine performance, economy (by 0.2l/100km or around 4%), the windows wizz up and down, and the headlights don't dim at all while cranking the engine. Spealking of which, the cranking power is hilarious, just bump the key and you're up and running immediately. When I hear someone else start their car I now always wonder WTH is wrong with it - oh yeah, a lead starting battery.

BTW, I'm using a standard car battery charger, all the decent ones come with LiFe modes these days, so I don't think I'm the only one in the world to have made the switch.

I've been using Li-XX batteries since they came out. I've probably got a couple hundred cells in total. More flammable chemistries (Li-Poly) are found in kids toys, so I'd suggest the fire risks are pretty low.

It works great for me. It's not for everyone and it's not for every possible contingency, but it's the best $200 I've spent on a car in a long time.

Full Disclosure: I killed my first DIY LiFe (14.4Ah) in my Fiat by leaving it parked for a couple of weeks. The stand by currents are high. However, I also killed the first Pb battery (60Ah) when I again left it for a couple of weeks. So I'm actually calling that a draw. Lesson learned. If you have a new car, you have to connect the charger regularly. At least on a semi daily driver, the LiFe needs no charging, while the Pb still does.

I wonder if climate is a big difference in our experiences and views. I've never had to routinely recharge a car battery. The few times I have is because of either a fault, the car was left for more than 4 or five weeks without being used or I'd left the lights on. Lead acid self discharge increases with temperature which makes them poor in your climate. Conversly they perform well in sub-zero temperatures so are good in northern europe. Same goes for the charge restrictions on LiFePO4, 0 deg charge limit is an issue for northhern Europe but not for warmer climates.

Robert G8RPI.

Just thinking about that 'rule of thumb', it really depends on what your usage is. For a race car or motorbike 1/10th OEM capacity will deliver more than enough cranking amps. If you're a caravaner and plan on using them for their reserve capacity - it's more like 1/2 or an AGM. A street driven car lies somewhere in between, depending on how you use it.

Remember too that standard Pb batteries are over size because they're not supposed to be deep cycled so really that 60Ah battery would have been a 30Ah.

Modern cars are right at the limits of 12v tech.

I wouldn't put it down to climate. I'd say whatever you pick up with cold weather battery performance is more than compensated buy having a cold engine, cold thick oil, glow plugs, use of lights, wipers, demisters and so on.

My Jeep used to sit for months without being touched and the battery lasted 11 years.

But I've now set up my garage with solar panels so all I have to do is connect the quick connectors, so why not?

I didn't NEED to charge the Proton battery regularly - it was more that - A. It's a good thing to do. B. It got me a handle on how much energy is lost in the inefficient chemistry. The Pb was only a year old and in fine health, but the LiFe were on a crazy sale.

Pb charge efficiency is said to be 85% -Li often claims 99% though I wouldn't put it that high, but it's very high. With only ~85hp (NA petrol) and a payload of 600kg (which I do use), I can feel if the A/C kicks in or the Alt is charging hard - the alt is doing a lot less work now.

My first LiFe install a few years ago in my 500 was a bit 'mad scientist' as I had to source the cells, make a case, add battery terminals, and rig up a BMS. Charging was with a hobby type charger.

These days I'm running off the shelf motorcycle batteries in parallel and charging off a standard charger from the local auto parts shop. Times have changed quickly.