I have two 6 volt batteries hooked up in series for my 12 volt house power on my RV. Both batteries were testing low with a hydrometer and a multimeter as a double-check. After using a basic car charger for several days one battery was testing in the 3/4 charge range on all three cells with the hydrometer but the other was consistently only 1/4 charge on all three cells.  Several people on the iRV2 forum suggested I try the BatteryMinder because they had good results and liked the product.Before I talk about my experience with the performance of the Batteryminder I thought I should mention the proper hookup procedure of a charger on a typical RV setup. Most people with batteries connected in series probably know how to properly hook up a battery charger but I did not. To help anyone who is interested in the correct method, I uploaded a photo of how properly hook up your charger. Do not hook up a charger where I have placed the red X's or it will not work. Note that if you have a temp sensor supplied with your Batteryminder it can go on any post including the ones with the red X's or somewhere close to the battery (however it is best attached to the battery if possible according to VDC tech support).After I connected the Batteryminder and let it run for a full 72 hours I am happy to report I had some good improvements on the batteries. After disconnecting the Batteryminder you should let your batteries rest for 12 hours and then test.  The hydrometer showed each cell on one battery (the right battery in the photo I have uploaded) was at 1.265 which is a full charge. The left battery is the one I mentioned before was showing only 1/4 charge or 1.155 in all three cells.  Now two of the cells (the right and left) were showing 1.265 which is full, however one (the center) was showing 1.225 so that was still low. I reconnected the Batteryminder for another 72 hours to see if the final poor cell improved. After the 72 hour run and a 12 hour rest I am happy to report all cells are testing at 1.265! I waited 7 days without using the batteries at all and retested every cell... again everything tested perfect.To wrap up this review I wanted I thought I should give props to the company for running a nice tech support department. I made one call and sent one email with questions to VDC Electronics (the company that makes this product) and wanted to note that the phone call was answered within 2 rings by a real tech support person with the help I needed and the I sent email was replied to by a tech named Wayne with an answer to my question within 4 hours.I am sold on this product as a good investment for my very expensive batteries and am very happy.