With LiFe batteries in a series-parallel configuration, it is not possible to balance each cell individually, as the paralleled cells cannot be electrically separated. They're physically bonded together.

Fortunately, this is not a problem, as cells in parallel tend to mutually self-equalize.

For any given pack voltage, the number of cells in series will always be a constant. In the case of a 13.x volt pack, there will always be 4 cells in series. Additional capacity (in Ah) is thus created by paralleling groups of 4 cells. So an 8 cell pack will always be 4S 2P, a 12 cell pack will be 4S 3P, 16 cells will be 4S 4P, etc.

Thus, regardless of the total number of cells in the pack, the number of balance leads will always be 5 (the total number of end-points of a series string of 4 cells.)

This is how all LiFe BMSes are configured.

D'oh! No excuse, total brain-fade in my post from last night. Of course any 13.x pack is 4S. Thanks for correcting me!

I still find this whole concept kind of hard to grasp.

I mean, they obviously work. We have proof of that.

It's the concept that, as you said, you can just throw one into a car with a 65 amp alternator and series-charge it t your heart's content with no internal balancing that seems odd.

That, and the fact that they apparently don't support an internal LVC to prevent the thing from being destroyed by dark currents. I suppose that would be difficult, given that you'd need a switching device that was capable of passing starter current and yet didn't require gobs of power to operate.

Which version of the Ballistic are you using in the miata? 8,12,16?

8-cells in the BP-powered race cars, 16-cells in the LS-powered race car.

Thanks! Would you foresee any issues running a 8cell in a daily driven STS miata?

I've been running a 12 cell in the SSM car. I'll probably upgrade to the 16 cell soon. The 12 cell has trouble cold starting the 1.8 on an AEM with the stock crank trigger wheel (takes 8-10 seconds to catch). If I could get the 12 tooth wheel working, it'd be fine on the 12 (maybe even the 8,) but as is, it's a little scary if it'll start before the battery stops cranking.

Depends on your climate. You might consider sticking a jumper pack in the trunk for cold mornings.

For a DD, if you're really pedantic enough about weight to get something this tiny, I'd definitely go no lower than the 16 cell. It's ~1 pound heavier than the 8 cell, and gives you way more cranking power. In a perfect world, you could get away with the 8 cell as long as you're above probably 60 degrees for 99% of your cranks, but I wouldn't want to risk it.

The big problem with these batteries for DD is just the lack of amphour capacity. They're much better than lead acid or gel batteries for providing more CCAs for longer, but when they cut out, they cut out dead. They don't actually have that much reserve capacity. So, you leave your lights on for a little while, it'll die, and way sooner than even a small lead battery.

Im running a 12 Cell It has way more cranking amps than any other small battery I have tried. and will crank the car multiple times roll up my electric windows with the car off etc.

Having said that The Heavyer NA starter will crank the car much more sucsessfully than an NB starter on a weak small battery.

Yeah -- the EVO2s definitely have plenty of cranking amps. They work fine right until you leave a light on. :)

I had a 180ma constant current drain on my car when I first built it. I plugged it in around 10pm and the battery was down to 5V the next morning. Woopsie.

I wonder:

Since we are talking about spending large quantities of money on lightweight batteries, I wonder why neither Ni-Cad nor NiMh have been mentioned?

Both are cheaper than most (all) of the present-day lithium technologies, and permit the use of rather simpler charge controllers.