What I've read so far has just confirmed my decision to skip on these jump starters. They don't work well enough to be reliable, IMO. And the problem they try to solve can be minimized through maintenance and routine. A pound of prevention and all that.


The biggest risk are IMO:
- Charging circuit not charging (mechanical or electric error). Check charging circuit as part of your scheduled maintenance.

- Battery failure: Too old battery. Check and replace. Also part of regular maintenance.

- Every day drive doesn't last long enough to completely recharge the battery. Consider topping up the battery once or a couple of times each winter season.

- Leave the lights on. You can minimize the risks through routine, but someday someone will foul this up. You could consider adding a cut-off switch (at 11-something volts) that supposedly turn off all power drain to save some minimum power so you can start the car. I've seen these in the shape of an extension cord for plugging into your 12v socket. The marketing typically sells them as preventing your piezoelectric cooler from draining your battery.

All in all, I consider myself good enough covered by jumper cables for the rather small risk of battery failure. If the jump starters actually had enough power to start my car with a totally dead battery I would perhaps reconsider.