WirthCo 20090 Battery Doctor 75 Amp/100 Amp Battery Isolator - Heavy Duty Dual Battery System for Trucks, RVs & Marine Vehicles - Black

My setup VW TDI.I bought this device for two reasons. The first reason is because I have a parasitic draw on my starting battery. The second reason why I bought this, is because I run a lot of accessories and I’m installing a second battery for towing purposes and the accessories. I bought an AGM deep cycle battery for the accessory battery. The nice thing is that I’ll be able to easily figure out if it’s just my accessories, or if it’s something running off of the ECU that won’t shut down. I am fortunate enough to have several leads, originally for the accessories, that run all the way to the rear. So now I can use those extra leads, to move one circuit at a time to the rear battery. The largest of course, is the four gauge wire to my stereo amplifiers. I just cut it in half where it ran through the cab of my vehicle and installed the device in between.The device.This works very much as stated in the description. There are only two small reasons why I wouldn’t give this a five out of five. The first reason is that it doesn’t come with something to cover the positive terminal’s. Again that’s a small thing. The second thing is that it starts charging the second battery faster than I would like. I’m getting exactly 14 volts off of my alternator. It detects the 14 and immediately starts charging the second battery. It’s somehow supposed to detect the true voltage of the first battery and not start charging the second battery until a certain voltage level on the first battery is present.However, the fact that I only have to hook up the positives from each battery to this unit and then a simple grounding of this unit, makes this something I can easily live with. It would at least be nice to have some kind of manual override. This might sound strange. However I installed this on the interior of my car. This way I can just reach over and manually hit the switch to connect both batteries, for easy starting if the first battery is low. This works very well.New Info! That parasitic battery draw that I mentioned earlier. It’s worse than I thought. After leaving town for a few days, and returning, my starting battery was down to 3 V. I thought great I have this new gizmo, so I press the button so that I could drop current from my secondary battery. Well the starting battery needed more than 150 A to turn it over. Therefore I blew the fuse. However I did not ruin the isolator itself because of its built in circuit breaker. After doing more research, maybe what I really need, is a continuous duty solenoid. Again, this device is working as it was designed. It would be nice if I could pull more than 150 A though. If they made one that could draw say 400 to 500 A I would’ve been much happier. Of course that may not have been enough to turn over my engine considering the starter battery was for the most part, completely depleted. Also, I was not aware that an isolator create a voltage drop going to the second battery. I am not just talking about the drop because of the length of the cable run to the rear of the vehicle. The isolator it’s self induces a bit of a voltage drop. Apparently solenoids do not from my research so far.If you’re running a second battery, I’d highly recommend getting this. You want to hear it, here it goes.This is a smart battery isolator, charger, and jump starter all rolled into 1 palm-sized device. When installed correctly, you can run power into your secondary battery without affecting the main starting battery. The device stays on for less than a minute between shutting off your vehicle and running parallel with your main battery. So there will be a small parasitic draw for balancing both batteries during that minute.This compact device has 3 connection points, main battery, secondary battery, and pre-wired ground. I highly recommend using a fused 4 gauge or higher cable from the main battery with the fuse or breaker fuse closer to the main battery, and a fused same gauge or lower wire out to your accessories from your secondary battery.Following the instructions I realized it wasn’t charging my secondary battery and wondered why. I later found that my main battery was faulting and after charging it for 8 hours didn’t hold a charge past 64%. With that said, it will only charge your secondary battery IF your main battery is charged past 13.4V.Once I got my main battery sorted (new one), everything was working as it should be. FYI, if either your main or secondary battery loses connection, the isolator will shut off by default. I tried to run the isolator in override mode to swap out the main battery without losing power, but found out that it simply shuts itself off. It’s a good thing.I also found out that this thing has a built in voltage spike regulator, similar to a power conditioner. But I wouldn’t consider it to be a conditioner either. Before this, I had an 80A Stinger battery isolator/relay between the main and secondary battery. I also had a 150A fuse breaker between the secondary to my rear fuse box for my accessories that kept tripping only during vehicle startup without any accessories ON. Battery to battery was fine over 80A relay, but the surge of power introduced by the alternator kept tripping my 150A breaker. After installing this, I had my 250W light bar ON running out of the secondary battery without tripping the breaker during startup. So in short, it can detect power spikes and send the correct signals.I highly recommend this if you’re into the whole secondary battery and trying to stay within budget. What’s $53 compared to potentially burning your entire electrical system (undercharging or overcharging) or getting stuck in a remote place without jumper cables.Hopefully this helps you think about what this thing is actually doing and what you’re protecting. I have a truck with a V8 5.0L engine and a stock 150A alternator, and the 125A/150A works for me. V6 and smaller motors with smaller applications can easily use 75A/100A system.Like other user mentioned, there are two cases this will not work correctly.1. When solar is connected to my aux battery, it will keep the main battery also charged so the voltage won't drop to disengage the relay. This is fairly okay because it's charging both my main and aux battery.2. When my aux battery (lithium) is full at 13.x Volt, even I turn off engine the isolator will still think it's charging and keep the relay engaged. It won't disengage until my aux battery is down to 12.x for at least 30sec. This is NOT okay because it will also drain my main battery without alternator on. The relay should disengage right away regardless the aux battery voltage to save main battery.I don't think it works properly.I previously used a cole hersee on my last truck.it worked great but required external switches and led. This unit is smaller, cheaper and required no extra switch or light.Seems to work great and is electronic vs solenoid so time will tell Very pleased so far 2020 chev. suburban, install required 2 x 150 Amp breakers plus 30 Amp breaker hard wired to trailer feed. The second battery in the truck powers and recharges my trailer battery and allows effectively endless use as every time we drive the truck it recharges the battery and then we can reconnect to the trailer using extension cablethe ability to boost the truck is a nice bonus which saved me on my last truck as the battery aged but this one is still young and the battery isn't dying yetupdate.. year later 8 camping trips 50,000 kilometers more on the truck and this unit is working great very very pleasedThis thing is amazing. I have it in my sidexside and it works perfectly. Keeps my batteries both charged and as an added bonus it allows me to boost my main battery if ever needed by just pushing a button.*** Update****It's been almost a year now since i've installed this in my Can Am, and it still works flawlessly and has saved me twice now with the Boost feature.once due to my main battery going dead on the trail and I was able to boost myself to start up and drive home.Second time, I parked my Can Am for an extended time during cold winter months and forgot to remove my batteries. I went out to start and it was way too dead. One little push of the button and my Machine sprang to life and I was off and running.I will 100% buy more of these to install in my truck,boat and Wifes Polaris as soon as the price settles back down. I paid $83 for mine in April 2019I had to buy a battery isolator because I had a small draw on my main battery. It was very nice, and useful. It isolated the second battery from the first battery 100% . If my first battery was completely dead, I just popped the hood and push the button and the vehicle started without any problems . Installation was as easy as it gets, and everything you need is included. Shipping was fast, and this thing worked very well in the coldest environment of Canada .Perfect dual battery setup for vehicles not all terrain machines like atvs or SxS.My truck has this and was a great setup.My SxS sits for an extended period of time, and this isolator drained both batteries. It has a constant draw on the batteries and won't notice it if you use your vehicle often. For my needs, won't put in SxS. Went with a true isolator, and now my batteries don't drain after a few months of sitting in the garage.