How does that work? If the battery stops providing current to prevent itself from being fully drained, you're not going to have power to the car's computers to actually start anything.
It will know when the internal batteries are running low (the internal charge/discharge monitor IC doing battery "gas gauge" measuring). It'll maintain a reserve of a few crank's worth of energy, and trigger shutdown before that's exhausted.
It can also tell if the engine is running, because the alternator will be, and charging it. It can also monitor the active discharge current.
If the battery is low and there's a small but fairly constant discharge, it's probably lights/radio, and a timeout of an hour might be reasonable.
It could then either cut power completely, or regulate discharge current to a couple of milliamps or something, just enough to sense teh spike when the starter motor is switched in. At that point, it switches in the supercap or goes back to full power 12v mode, and the starter gets cranked.
The only downside I can see is that fully isolating the battery may have side effects that upset the ECU, radio or immobiliser system (I recall our radio would go into 'presumed stolen' mode if fully disconnected and require a PIN to work properly, I have no idea if/how that happens in modern cars though)
A "dead" lead-acid battery often isn't dead enough for that to happen, just htat it can't supply the ~200A that the starter requires to crank.
How much safety testing have you done on your battery? Specifically, if an Ohm battery is involved in a collision, how will it fare? I know you are not content with shipping anything you aren't comfortable with your own family members driving with [1]. But, how do you know this? What makes you so sure? I don't mean to come across as interrogative - I am just curious.
edit: grammar
I have no idea if this ends up being a significant number, but I think the average driver spends somewhere around $10k in fuel over the expected lifetime of this battery; if cutting down the weight by 1-2% reduces fuel consumption by a comparable amount then Ohm would pay for itself.
I was going to say, for the first iteration of the product you could consider using classic lead-acid instead of LiPo. It's cheap, so it would help keep you price-competitive. It's absolutely proven as an automotive battery chemistry.
The difference vs. a classic battery would be, your smart circuitry to shut off the battery, and the cap stage would allow for a tiny battery even on big engines. Your LiPo model already sacrifices capacity, and the only other reason for a big battery is CCA, which the caps solve. Thus you could put an itty-bitty 10Ah lead-acid in an F-550. Bigger & heavier than a 10Ah LiPo? Sure, but still way smaller and lighter than modern F-550 batteries.
You could then move to LiPo for later versions as you get the truly novel parts of the product dialed in and costs starts to come down.
I'm trying to understand what the barriers are.
Industrial motors aren't something I've looked into a lot yet, but it could be interesting. I was just talking with someone the other day about using supercaps in robotics applications. Apparently some people are already putting small supercaps in the joints near the motors to help provide surge current during high accelerations or loads.
I have an older car with occasional electrical gremlins. My battery is fine, but an ounce of prevention...
http://www.cnet.com/news/pocket-sized-jump-starters/
(linking the review because I don't know which brands are reasonable...)
Stricter regulations on shipping methods than for other cell chemistries. Degrades at high temperatures.
However, for Lithium Iron Phosphate LiFePO4: "Lithium phosphate cells are incombustible in the event of mishandling during charge or discharge, they are more stable under overcharge or short circuit conditions and they can withstand high temperatures without decomposing."
We believe so, but don't want to say it until we can verify for sure. Our temp chamber unfortunately has trouble pushing anything south of -20F and it's a bit hard to find weather that cold in August.
There's a few other vids on this topic if you search through the channel
-22F ~ -30C
They are always looking to shave off weight so it can be redistributed in the way they want. Being able to cut 30lbs would be a big deal.