People either like these or they don't. No in-between. I like them, a lot. Permanently wired in my motorhome with a CTEK (56-677) D250S 5-Step, Automatic DUAL 12 Volt 20 Amp Battery Charger. Very simple wiring, nothing to go wrong. Starter and house batteries charge off solar or alternator or AC current via another CTEK product - a 15A charger. With a battery monitor and Blue Sea Systems ST Blade ATO/ATC Fuse Blocks, a maze of complicated wiring and devices became very simple and reliable.

I have no particular beef with the product, other than it failed after 1.5 years in use. As the manual instructs, I installed it in an open space. It was mounted on top of a piece of aluminum plate attached to the underside of my trailers A Frame. It was protected from everything but precipitation, from which it was supposedly sealed. It quit. I pulled it off the trailer and could hear water sloshing around inside. I opened it up to drain the water out and dry it as its seal had obviously failed. Yes, I broke "the seal" (little red thingie on top of one of the screws) which in CTEKs eyes apparently makes me a horrible awful person who deserves no consideration or respect. Anyway, I dried it out and tested it. Still not working. I wrote an email to CTEK explaining, in detail, what occurred and was instructed to sent it in for evaluation. I did so. A couple of weeks later I received the unit back, unrepaired, with a letter explaining that since I took it apart it was not covered by warranty which was already expired, anyway. They stated that my warranty had expired because the unit had been manufactured in 2012. The fact that I purchased it via Amazon on 2015 and should still have been covered by the 2 year warranty was not relevant to them.
Moral: Good product. Stinky company. Customer service is unworthy of the word service. I wont buy another one. Once burned, twice shy.

Between this and the d250s, I couldn't ask for more and even better, easier. I have a 300 amp hour battery bank, which requires more than the 20amp limit of the d250s. With the SmartPass, I can get more amperage from my alternator) into my more deeply discharged deep cycle batteries. Otherwise it takes too long and is inefficient to charge the batteries. And chronic charging insufficiency will kill your batteries slowly. And if there are multiple deep cycle batteries, that means you have sunk plenty of money into them. The SmartPass will save them by allowing them to be charged more deeply and quickly. Keep in mind that you'll never get a full charge from the alternator unless you drive hours at a time. That's why the solar input on the d250s is so important-the solar will finish the charge with a long, slow trickle. The d250s and the SmartPass make a wonderful system if you want an easy solution for a complex system that is needed if you are going to be spending time off grid and want to love your batteries.

Did everything as claimed. Easy as pie to install.