I live in Arizona and battery starters don't take the heat very well - to be honest I forget to charge them too. The 12v battery for my car ended up in the trunk which doesn't open when the battery is low/low. Oops. Enter this small device that perfectly suits my needs. I don't have to maintain it and just need enough amps to close the relay to the main battery in the car. Luckily there is direct power under the hood (first photo). I was able to charge the device with a portable USB power bank, which is very convenient. A small LED on the front can be turned on by pressing the flashlight button. The device needs to be turned on (press the power button once - you should see % and hear a click) when charging via clamps, 12V (with cigarette lighter) or USB - at first I almost thought the device was defective. Relatively fast charging with battery or cigarette lighter adapter - takes a little time via USB. Added some photos of 300mini as I couldn't find anything online. Update: 10/01/2019. this morning. Added new picture, my battery was only 6.4V, on the LCD. However, had charged up to 100% and allowed me to start the car in minutes. Update: 12/11/2019 - A colleague from Toyota Tacoma jumped it on, his battery was at 5.8V and didn't even charge the unit. It took me less than a minute to charge it up from my car and light it up the first time.