BMK 12V 5A Smart Battery Tender and Trickle Charger for Car Motorcycle Marine Boat - 4-Stage Fully Automatic Battery Maintainer for Lawn Mower Deep Cycle AGM Gel SLA Lead Acid Batteries

If your have variation of voltage from the utility (100-240), this product works as designed. I am a photovoltaic technician and use it to keep battery toped of & if a battery is lying around--it will prevent it from getting sulfated. I reached out to a name brand & I was disappointed that the rep (owner/ceo), didn't even know that his competitors have the voltage variation available like this offers. It prevents it from killing the power supply (charger) if you have constant voltage sages. I waited some time before evaluating it. It charges up to 14.4 vdc (for agm & gel batteries) & back to 13.6 vdc after the battery is charged (floating)--as it should. Have been using it for various weeks consecutively w/o a hickup. Update: I purchased a 2nd unit to maintain my 2nd car's battery & the other unit has been reliable. I recommend this unit. Works as designed, a very good price, I have had the original one connected weeks straight day-after-day. Worthy buy. Update #2: have been using this unit for months straight in a row DURING HEAVY voltage sages & outages AND OVERVOLTAGE situations (scarry situations) and to my surprise--still ticking as expected (better than). I have two other chargers doing maintenance for car batteries and I now have to purchase a replacement units (plural) for that usage. The only reason I don't purchase 1 or 2 more of this unit is because I need a higher capacity. I am going to look into seeing if this manufacturer has a higher capacity... i do like to give credit for a good quality item for a fair price. Good purchase

I saw reviews of how difficult it was to find instructions. Then I scrolled down on the Amazon page and found two pdfs for the Installation and Operation Manual. What could be easier than that? Directions are great and explain the led lights and what it is doing at each point. I like LED's better than garages. Much easier to see and use. For those who say it didn't work or charge for them if you read the instructions, it says if the battery is lower than a certain level it won't charge. I think it was either 1.5 volts or 3 volts. if it is lower than that then the battery might be bad. Also, this will stop charging after 72 hours and go into float mode. It is for safety. Not bad and you don't even have to think about it. Pleased with my purchase. I just wanted to put a car's battery on a charger for the winter and forget about it. Operating temperature range -5 F to 120 F. Additional info: Just bought my second one. This charger not only kept my battery from dying it rejuvenated an older battery. So I'm getting a second one for the Truck that sits throughout the winter.

So far I have been really happy with this battery maintainer. My Nissan Armada has a slight parasitic drain on the battery that will kill it if I leave it sitting for a week or so. I mounted this charger under the hood next to the battery and ran the power plug out the front grill. I then plugged it into a timer that only runs for about 4 hours a day. I purchased it in September, and so far it has worked through a very snowy winter where temperatures have gotten as low as -20 below zero. I don't think it has gotten water directly splashed on it, but I have driven through pouring rain and car washes that spray from all sides of the vehicle even from underneath. So far I'm impressed with it. Update, Sold the Armada and moved the charger to a small car we keep as a spare. It sat for most of the year through sub zero winter days, and started right up when I needed it last month. I bought a second one for my pickup and it has worked great. I ran into an issue where I killed the battery while trying to jump start an old diesel plow truck, (one of the cells had intermitant activity) and the charger indicated the fault. After getting a new battery it has kept my pickup charged through one of alaska's coldest winters. I'm ordering a third one for my plow truck as I only use it a few times a year.

I've had this charger just over a year now. In 2020 I stayed home a lot and drove less than 1000 miles for the entire year. My car was frequently parked in the garage for 1 to 4 weeks (or more) at a stretch without being driven. And oftentimes trips were local and quick without enough drive time to recharge the battery. I found that after about 10 days of sitting undriven, parasitic draw would reduce my battery's voltage below 12.6V. The charging and maintaining features of this unit worked really well to keep my battery charged up and reliable. Only once (the first time) was the battery below 12.5V. The BMK charger did what was expected and never got more than barely warm during the 8 or so hours it was charging, then switched to float mode. The battery itself never got warm either. Good job! All the rest of the times I've used it, the battery was between 12.5V-12.6V when I connected the charger. As expected, it took care of charging and went into float mode. BUT 5 times during the year it did something unexpected: it turned off a few hours after doing its typical routine. I have no idea why. The temperature in my SoCal garage was always moderate or cool. When I'd see it off, I'd check AC to the changer (always on) and would completely disconnect the charger from AC and the battery. Checking battery voltage with a VO meter, it was usually between 12.8V-13.1V. After re-connection of the battery to the charger and then charger to AC, it'd still not turn on. So weird. The first time it happened I was sure it had died. But a couple hours later I tried again and found it worked just fine. More weirdness. But in a good way this time. Just recently it turned itself off for the fifth time in the past 13 months. Once again, I tried to reconnect it right away to no avail (which is what I expected). After leaving it disconnected for a couple hours, when reconnected, it worked like it was brand new. It seems to have an occasional, mysterious reliability problem. That's why I'm knocking off one star. Except for that issue, this unit has been a great help keeping my car's battery ready, even when I've not driven the car for weeks. (As long as I check on it every few days to be sure it's not turned itself off.) Update June 2022 -- It's still working just the same. Most of the time, it does just what I expect. But about every 5th or 6th time I use it, after several hours (maybe overnight or a day later) it turns itself off (and battery voltage is about 12.7V or so). After that I have to leave it unplugged from AC for at least an hour or two, then when I hook it up again, all is fine and it'll work as expected until I need to drive my car again, maybe 10 or 14 days later. Except for the mysterious turn-off glitch, it's a good product. But because I don't have confidence it'll always have my battery charged and ready, I make sure to check voltage level a day or two before I need to drive somewhere.

I was initially sceptical about the product and whether it would actually work as described; because of the low price. My fears were unfounded and I was pleasantly surprised to find that the product was easy to use, value for money and worked as described. The battery on one of my vehicles was totally dead. The product charged the battery from dead to about 80% in about 7-8 hours! The product has four LED charge lights which indicate the level of charge achieved during the charging process. So far, so good! I would recommend the purchase of this item to anyone.

I may have a defective model, but the battery simply wouldn't charge. I thought maybe I was wrong and tried to jump my car with it - nothing. The email provided in the instruction booklet does not appear to be in order. I very carefully typed it and double/triple checked it, but it came back "address not valid." Then I emailed the company that is selling it via Amazon. There is a phone number but I ain't calling China. I asked them to please call me, figuring they must have some kind of economical system set up to call foreign customers. No call but they did reply to my question with a couple suggestions to test the charger. One was to plug it into the power source and if the charger light turned green, the unit is good. The charger light was red, as I had told them it was. Then they told me to clamp the two clips together and if the charger light turned red, the unit was good. I emailed them back to be sure I understood correctly because that sounded kinda strange but they wrote back and said yes, that's what they wanted me to do. Well the charger light was already red, because that's what happens when I plug it in. It stayed red when I attached the two clips to each other, though the led charging % indicators went crazy, as one would expect. Not sure what the purpose of that exercise was but the fact remains, I bought this item because I needed it. I had a battery that was losing its charge periodically leaving me in a bad spot at times but since I will be getting rid of the old heap in a few months, I did not want to invest in a battery. My car was sitting dead in the driveway, the precise situation for which I bought this thing, and I still had to call someone to come charge it because the charger I purchased wasn't worth the postage it took to send it to me. Amazon is sending out a new one. But regardless of whether that one works or not the point is that these things should be quality checked before being sent to customers. A defective charger is no better than no charger at all. There seem to be a lot of reviews starting the item they received was defective, defective products should be very rare. I wish I'd taken all these reports of defective items as a warning. I am most unhappy and their customer service is downright useless.

I own three of these and love them. I keep them on my two cars that I don’t put many miles on, and use the other to recharge other cars if they get low.

Today's cars are constantly draining the battery with always on electronics. Working from home means not driving as much, so your car battery may, or may not work when you need it. This product makes sure that when you want to start your car, your car starts. My battery was completely dead, to the point this device did not recognize it was connected. I had to jump the car with another vehicle first and let it run to charge the battery. After the battery had some charge the Smart Battery Charger Portable Battery Maintainer completely charged the battery and the next time I needed the car, it started right up.