Review on WirthCo 20092 Battery Doctor Isolator by Scott Gamache

If you use a second battery, I strongly recommend getting one. You want to hear it, here it is. It's a smart battery disconnect, charger and jump starter in one palm-sized device. Properly installed, you can power the auxiliary battery without affecting the main starter battery. The device stays on in parallel with the main battery for less than a minute between parking the vehicle and turning it on. Therefore, balancing both batteries during that minute will have a small parasitic load. This compact device has 3 connection points: main battery, secondary battery and upstream ground. I highly recommend using a 4 gauge or better fused wire from the main battery with a fuse or a fuse closer to the main battery and a 4 gauge or smaller fused wire from the auxiliary battery to your accessory. I managed to do it following the instructions. I didn't charge my extra battery and wondered why. I later discovered that my main battery had failed and was not more than 64% charged after 8 hours of charging. Aside from that, it only charges your secondary battery when your main battery is over 13.4V. After (re)sorting my main battery, everything worked as it should. FYI, if your primary or secondary battery loses connection, the isolator will turn itself off by default. I tried running the isolator in lockout mode to replace the main battery with no loss of power, but found it would just shut down. It's good. I also found that this thing has a built in surge stabilizer, similar to a voltage regulator. I wouldn't call it a conditioner either. Before that I had an 80A Stinger battery isolator/relay between the primary and secondary batteries. I also had a 150A fuse between the secondary and rear fuse box for my accessories that only blew during auto start with no accessories on. The battery to battery connection was fine with the 80A relay, but the surge generated by the alternator kept tripping my 150A circuit breaker. In short, it can detect surges and send the right signals. I highly recommend this if you're using all of your secondary battery and trying to stay on budget. Which costs $53 compared to burning up your entire electrical system (undercharging or overcharging) or being stuck in a remote location with no connecting wires. I hope this helps you to think about what this thing actually does and what you are protecting. I have a truck with a 5.0 liter V8 engine and a stock 150 amp alternator and I have 125/150 amp. V6 and smaller engines with smaller applications can easily handle a 75 amp / 100 amp system use.