Review on 🔋 NOCO GENIUS2: Advanced 2-Amp Smart Charger for 6V and 12V Batteries - Battery Charger, Maintainer, Trickle Charger, Desulfator. Includes Temperature Compensation. by Shigg Bigbee

I have a 3 year old 12v AGM battery that has taken a lot of abuse as I only drive 4 miles to work and only do longer trips every two weeks. Lately I've been staying at home because of the coronavirus and driving out about every three weeks. Needless to say, the battery died and I couldn't start my car. All lights went out when the car door was opened. I bought Noco Genius2 to try it out. I was amazed at how small it was. I checked my battery with a voltmeter and it was 1.9v. I plugged in the Noco Genius2 and the first LED started blinking and showed less than 25% charge. I've found this Noco to be rated at 40Ah and my car battery is 80Ah, but I've read reviews that it should still work, it just takes longer. Well I left it on for about 20 hours and the first LED never stopped blinking. I checked the battery with my voltmeter but the voltage was jumping all over the place so I figured maybe desulfation was going on. Desulfation can take a long time so I left it on again overnight and the next day the first LED was still blinking. I unplugged the Noco to measure the battery's DC voltage and the voltage reading was 0. At this point I was becoming very disgusted, thinking that either the battery was beyond repair, or the charger was defective, or maybe I have a charge on the battery (like leaving the headlights on, but I knew they weren't). I decided to disconnect the ground clip from the battery clip to try again. The voltage reading jumped to 4.2V with the ground clip disconnected, so I didn't have to use the forced mode on the Noco (it's a special mode that forces the battery to charge when the battery voltage is too low). I ran another 20 hours and the first LED would not stop blinking and showed less than 25% charge. I was ready to give up that point, so I unhooked the noco and measured the battery voltage - lo and behold, it showed 12.3V. Good things were happening, but I didn't understand why the second LED wasn't blinking. (indicates between 25% and 50% charge). After about 5 hours the second LED blinked, a few hours later the third LED blinked and after another few hours the fourth and last green LED started blinking indicating 75% to 100% charge. I left it plugged in overnight, but the next day the green LED wouldn't stop blinking. I ran it another day and the next morning the green LED was still blinking. According to the user manual, it is sold with 100% charge. At this point I unplugged the noco and measured the voltage - it was 13.3v. Not super awesome but over 12.6v when I was able to start the car. With the ground terminal disconnected from the battery terminal, I took a reading on the amp and it drew only 13mA, well below the 50mA I would be concerned about. I connected the ground clip and was able to start the car and I think the battery is fine now. I was really impressed with the Noco's ability to recover the battery, which seemed to be in pretty bad shape. I think the manual should say that the battery should be disconnected if the voltage is too low - that certainly helps with charging. If you need faster charging, don't buy Genius2 either - buy Genius5 or Genius10. In my case, I didn't care that it was going to be two weeks because I wasn't going anywhere. And if you stay at home because of the corona virus, drive every now and then. But now that I have the Noco, I can just leave it plugged in.