I returned to my car at 12:50 AM at the airport after being away for 8 days to find a dead car battery (left the interior light on when getting all my luggage out)in my Honda Hybrid. Despite the hybrid having an expensive, humongous high-voltage, high-amperage battery to run an electric motor, there is no thought given to using it to back-up the plain old 12-volt battery used to start the motor. Probably this is intentional to keep it from ever being fully discharged.

A fellow passenger kindly hooked up his jump-pack, as he had had a similar problem himself and wanted a way to be able to get himself going without relying on someone else. He had stopped carrying jumper cables.

His jump-pack was dead; his chagrin palpable.

My jumper cables got the car fired right up.

The jump-packs do require regular recharging/checking; they're something else to check once a month. I've got more than enough of other things to do that I don't need to add that annoyance.

I'll stick with the jumper cables for my needs, as it's rare that I'm not around someone else. If I was way off in the boonies by myself, then I might make the financial plunge.

Sometimes, it does "take a village".

Or, I coulda just called AAA.

Keeping in mind the last time my battery died of old age -- not a graceful degradation, it simply died and would not take a charge -- I replaced my battery 'cause I felt it was time and the truck was already in the shop for other routine maintenance. I prefer to not have the hassle of doing it when "I really don't have time for this". Don't have a supplemental charger; I do have road service, although not AAA.

These sorts of units have some utility.

A year back I was in a tire place waiting for them to slap new shoes on my truck and a lady comes in and asks the guy manning the desk if she could get a jump. Now this place was mostly a tire store with minimal capacity for repair. A good place to get compressed air for tires but not the place I would think of getting a jump. I was just about to offer to help, they hadn't pulled my truck into the shop yet, but the man at the counted said he would help, So he leans into the garage area and grabs one of these battery units and follows her out the front door. He reappears after a few minutes.

After A bit I ask him about it and he says that it happens all the time. Somehow people just figure that if you work on cars you are set up to jump-start one. The owner of the business, working the angle that doing people the favor of getting their car started was good advertising, arranges to keep a couple of the units charged and ready to go.

I thought they might be special commercial units but when I went into the work space what I saw was the same units you can buy at any discount store. They were the top of the line for discount store units but they weren't anything special. One of the techs noted that the consumer grade jump battery units work pretty well as long as you keep them plugged in and charged. Most people needing a jump just need a little extra power and there gel-cell battery units are light enough to easily carry around a large mall parking lot.

After this I took to looking around all the garages I visit and have noted that a lot of automotive places, even parts stores, seem to have one of those units. I'm not sure they make sense for an individual home where, assuming the vehicle/s are well maintained, the times you might need it are few and far between. Particularly because the gel-cell will deteriorate over time.

An alternative might be to get an inexpensive battery charger. With the newer pulse technology electronics these units have dropped in price, size and bulk. Used to be even a small battery charger was a substantial hunk of equipment that was also a substantial investment.

The newer units are cheap and light. They also seem to work well and last so for a small price it makes sense to have one on hand.
Larger chargers have a 'jump-start' mode that will get you going fast but even smaller units will charge a mid-sized battery in an hour or two. The weakness is you need line power to run them. But if you know an emergency is coming, like the days before a hurricane, there is no reason you couldn't charge up all the batteries, possibly even a reserve or two, and have them all GTG when the time comes.

I have one of those plug in chargers. In winter time especially I plug it in every week or so to keep the car battery in tip top condition, especially now I don't drive it daily.

The jump packs I have used are ,as mentioned, a helper not a stand alone unit. I work at the Tire and Lube at Wally world, so I get to use the jump-pack at work a lot. It works about 75% of the time. I have found hooking up the pack, try it, if no dice then wait 5 minutes and try again helps. Personally I dislike jump packs, they don't pack the wallop that my little ranger does. experience has taught me jumper cables are the way to go for dependability. I have only seen jumper cables fail once (short in the line of a set older than me) but I had mine so no worries.
Of course you could just drive a manual transmission and roll start it. (guilty as charged, battery died a couple days before payday, so i parked facing downhill until i got paid )

I have used my battery booster dozens of times to start small and large vehicles but I also carry jumper cables as a backup.

It has been nice to have the booster pack when my car has sat at a trailhead in -30C for a week and there are no other vehicles around to hook cables up to.

The battery pack is also easier to hook up than cables as you do not need to maneuver vehicles into position which can be difficult in deep snow.

When traveling in really cold weather I also pack a battery charger and a long extension cord.

A friend drove a Pinto, what can I possibly say, with a dead starter. So he just parked it on a slope. Any slight slope would do. Even a 10' driveway. Starting was as simple as opening the door (He never locked it or took the key out of the ignition), releasing the parking brake, and giving it a shove using the door frame and door for leverage, once going a couple miles an hour he would turn on the ignition and pop the clutch. And off he went.

When my beloved VW Beetle had a dead battery and I was a bit short of cash, I did the same. Many moons ago....

To elaborate on my own situation:

I have a new battery (replaced it last January when the old one reached end-of-life), and I have a good set of jumper cables.

But I do leave the lights on once in a great while, same as anyone else, and the car doesn't have a warning signal.

So this is backup for when there's no one around to get a jump from, something I can try before I try to pop-start it.

I keep jumper cables in each car, a really nice set of 16' cables in the garage at home, and a jump battery. The battery is left over from a time before I had dummy bells on all my cars for the lights being left on. It is also handy for occasional outages; I can charge a cell phone, listen to the radio, and with an inverter I can run a fan and a CFL bulb for a few hours.

Of course, with all these wonderful things the last time I needed a jump I was in a rental truck and had nothing with me.