Batteryless Jump Starter - Jumpstarts Vehicles Using Ultracapacitor Technology for Cars, Trucks, Boats, RVs, ATVs, and Other Gas Engines (RZ-550 (550A))

I decided to try a supercapacitor jumpstarter because I didn’t want to have to worry about keeping a battery-based unit charged up for the (hopefully) rare times I might need it. I selected this particular one because it had an LCD status/voltage display and didn’t have the boxy dongles of some other less expensive models.As chance would have it, I had the opportunity to test it *twice* the weekend after I received it.The first time was when an out-of-town friend called to ask how to remove his Hyundai Genesis battery. He doesn’t mess with cars much and the battery cables on his Genesis were a little confusing to him. Coincidentally, I was on the road and would be passing within about two miles of his house. No lie! I told him to leave the battery in place so I could come try out my new gadget.I stopped by and found that yes, his car’s battery was dead dead dead and the starter would barely click. The Rezervo’s display showed something like 7 volts and it wouldn’t self-charge from his battery, so I hooked the unit up to my car to get the capacitors charged to 100%.It took us two tries to get the Genesis started because his battery was so dead. On try number one, opening his door and putting his foot on the brake pedal (required to start the car) were apparently triggering the Rezervo to dump its energy, wasting it on the brake lights before he could try to crank the engine. Here’s what we did to help the Rezervo do its job: I charged it on my car. My friend got in his car, closed the door, verified the headlights and AC were switched off, and put his key in the ignition but didn’t turn it. At that point I hooked up the already-charged Rezervo to his battery and made extra sure the clamps had a good bite on the terminals. I engaged the Rezervo’s override mode, which was needed because his battery voltage was so low. Then, in very rapid succession so as not to waste the Rezervo’s energy, he put his foot on the brake pedal and immediately turned the key to engage the starter. Sure enough, the engine cranked and started right up! So that was success number one, and at that point I was a happy camper and went on my way suitably impressed because the Rezervo worked as advertised and I didn’t have to drag out the jumper cables.As (bad) luck would have it, when I pulled into my driveway later that weekend I noticed my truck’s interior dome light was glowing, having been left on for several days while I was away. The battery had run down and trying to start the engine resulted in hopeless clicking from the starter. On the good side, now I had a chance to try out my toy a second time…This time I was able to get the Rezervo to self-charge off the truck’s battery without the help of another vehicle. It did take a couple of tries to get it to 100% , presumably because the act of charging up the Rezervo depleted the battery a little bit - the energy has to come from somewhere! - but giving the battery a little rest between tries seemed to help. I was determined not to use a second vehicle for help because I wanted to pretend I was in the middle of nowhere with no friends nearby.Sure enough, once I had the Rezervo at 100% I was able to start the truck right up - again sequencing things to minimize energy drain from things other than the starter. This is a genius device!My guess is that this works best for cars that generally start easily but whose batteries have gone dead-ish due to lights being left on or are a little marginal and have gotten pushed over the edge because of weather, etc. You’ll probably still need jumper cables if your car normally takes a lot of cranking to get it started.As other reviewers have noted, a carry case would be nice, but I just kept the original cardboard box, covering it in a layer of clear packaging tape for a little durability. It takes a little finagling to get the unit back into its box so it’ll close all the way, so pay attention to how the parts are arranged when you first open it.I give this a 5-out-of-5. It works as advertised, and just needs a little extra care in the sequencing of steps. It’s certainly a lot easier than having to drag out the jumper cables and being extra careful to not short them together, cross them up, or damage the electrical systems of either car. Surely I’ll still keep my jumper cables around, but the Rezervo will be the first thing I try for most situations. Jumper cables just seem so... twentieth century!

These super capacitors jump-starters are ingenious. The way work is that is uses the remaining power on your car battery (usually when your car won't start, there is still power left, just not enough) to charge that power into big capacitors, and then release that power all at once with high amperage for a brief moment so you can start your car. And then after that, your car alternator takes over. So basically, you connect this jump starter to your battery, wait a few minutes (will take a longer time if your battery is near dead, and will be pretty quick if it just lacks a little bit), and once the green light lights up, you can just start your car. If your car battery is completely dead, you can use other sources to charge the capacitors, such as an electrical outlet, another car's battery or the cigarette lighter of another car.There are several advantages:- No need to keep a jump starter battery charged. You can just forget it and then use it 6 months later when your car won't start out of the blue.- Works is very cold or very hot temperatures. If I left a regular jump-starter in the trunk of my car in winter at -20°C, the battery would most likely be as dead as the car battery when I would use it and be pretty much useless.- Much smaller and lighter than conventional, or even lithium-ion jump starters.- No battery to replace once in a while to keep it working, these capacitors should last a long time.The only disadvantages is that you need at least some power for it to work(would need to use other power sources if your battery is completely drained), and you need to wait a few minutes to start your car while a charged jump starter can be used right way. But at least you don't need to predict you'll have troubles starting your car. And of course, the capacitors will only stay charged for a couple minutes, because, well, they're capacitors, and that's not the way it's meant to be used anyway.I bought this because I have my work truck at home and don't use my car to go to work, so I can be a few days without using my car sometimes, and when I use my car, I usually don't drive too far with it(so the alternator just never have any chance to charge the battery enough). This was a big problem for me in the cold Canadian winters, my car battery would often be too weak to start the car, and it would always happen at the most unfortunate times, of course. Now I just keep this baby in the trunk of my car and I can pretty much always start my car within a few minutes. No need to find someone willing to jump jumpstart my car with their car. It always worked the way it should and has never let me down so far. I definitely recommend this.

It does take a charge from the car battery or mini USB (takes a long time to charge). I haven’t need to jump my car and can’t comment on whether it will help me in my time of need, but the quality is subpar. The holes for the mini USB port doesn’t line up. Feels cheap.Update: DO NOT BUY!!! Stick with cables. This product failed when I needed it to work. My car battery died while my kid had an iPad charging. So, I’d attached this batteryless charger to the battery terminals. It would charge itself to full, but it would drain as soon as I’d started the car with barely a few cranks. My car didn’t start. I tried repeating the process, but my car battery keeps draining each time. A Good Samaritan helped jump started my car. I’d even disconnect the cable from the battery before jumping with the Rezervo, but it would discharge immediately to the car’s electronics.

Super capacitors don't have to be maintained and pre charged like a battery that will lose its charge over time. You just connect it to the battery and if it has over about 8 volts (enough to turn lights on but not start the engine) it will charge the capacitor in about a minute or two and you can fire up your engine. These seem to have more instant power boost for the rating also. No more going to jump your car and finding out that your booster pack doesn't have a sufficient charge.

Sometimes you have to try a couple times in order for it to work properly. But overall, it’s a good product.I love that it can sit in the car all year long and be ready at any time.