Lazy Daze Owners' Group

For some time I've considered carrying a lithium battery jump starter in the toad, but I was reluctant because of dire warnings about high temperature damage.  For example, the Antigravity Micro-Start XP-20-HD user manual says "Do not leave the product in, or expose product to extremely high temperatures such as on dashboards or other hot areas above 110°F (43°C)."

One summer I kept a digital min/max thermometer in my car.  The maximum temperature it showed was 55C, which is the upper limit for the thermometer, so the actual maximum was probably higher.

I just found out about supercapacitor jump starters, and I started carrying an Autowit S2-7.0 in the toad.  The device is claimed to withstand up to 70C.  My understanding is that it's basically a DC-DC converter plus a bank of big capacitors.  You charge the capacitors, push a button, and then the capacitors discharge in a short time with enough energy to start the car.

There are three ways to charge the capacitors.  (1) from the "dead" battery itself.  The idea is that a battery too low to start the car still has some energy.  (2) from a cigarette light plug, presumably from another car nearby.  (3) from a USB cable.

I tried charging by USB.  It took 34 minutes.  The manual said it should take less than 30 minutes.  Charging directly off a car battery should presumably be faster, depending on the state of charge.  24 hours later I plugged in the USB again.  It was at 52% charge, and took 18 minutes to get to 100%.

This is not a review.  I've never used it, and with luck I never will.

The box lists the manufacturer as GenHigh Tech Co., Limited, 1355 Liuxian Avenue, Nanshan, Shenzhen, China.

And now for an absurd question: can an iPhone start a car?  iPhone 15 has a USB-C port that can deliver up to 4.5 watts.  iPhone 15 has a battery capacity of 12.981 watt hours, or 46.732 kJ.  To be conservative, say starting a car takes 200 amps at 12 volts for 3 seconds.  That's 7.2 kJ.

And now for an absurd question: can an iPhone start a car?  iPhone 15 has a USB-C port that can deliver up to 4.5 watts.  iPhone 15 has a battery capacity of 12.981 watt hours, or 46.732 kJ.  To be conservative, say starting a car takes 200 amps at 12 volts for 3 seconds.  That's 7.2 kJ.

Thanks for posting that "non-review." I too have an Autowit SuperCap 2 booster pack that I've never used. But I also carry a Noco GB40 conventional (LiIon) booster pack, just in case the Autowit can't milk enough juice from a dead starting battery.

But actually, now that I think of it, I also have a 105 amp-hour AGM battery that keeps my truck fridge running, and a 140 watt solar panel on the roof that keeps it charged, so I could always charge up the Autowit unit from that. But, well, belt and suspenders, y'know. 😉

The limiting factor is the 200 amps that the starter motor draws.

I mean, the iPhone charges the Autowit, then the Autowit starts the car.