I'm not especially bright, especially with electrical stuff, so bear with me.
TSP/F got me interested in battery backup, so I built my first one a few years ago.
It was basically two 6V 220Ah GC2 batteries from Costco, an oversized inverter, a so-so 4A 3-stage charger, and some cables and 400A fuse, all inside a flip-top crate on a dolly. I took pretty good care of it at first, checking the fluids regularly, using the battery every couple months, but most of the time it just sat in the utility room and pissed my wife off every time she had to walk by it. Then, one day while making a rare trip to Walmart, I noticed the big 55A Schumacher that I'd heard about on one of the Steve Harris episodes, so I bought it.
I managed to boil off enough water to expose the plates by the third time I used it, which instantly reduced the capacity of my battery bank to about 75% of what it had been. I was mad at the charger, but mostly just mad at myself for being so stupid for charging a 220Ah battery bank at 55A. So I decided to try something different and go with an AGM battery, different charger, and different container.
I wound up with a 150Ah Lifeline AGM battery and a 1500W inverter in a vertical rolling Pelican case. I also got a 26A Genius charger for bulk charging, and a smaller 1A Genius to keep it on float.
Overall, I was pretty pleased with the system in terms of its compactness and the performance of the battery and chargers. It was nearly maintenance free and a bit easier to move around than the previous setup, but still pissed my wife off every time she had to walk by it (of course, now there were two monsters in the utility room).
I then decided to try something inside my vehicle and decided to go with a couple of U1 batteries in parallel, an inverter, and an ISOpwr unit between the car battery and the auxiliary battery.
I was able to fit everything into a milk crate and used the 12V outlet in the back of my vehicle, instead of pulling another separate cable directly from the car battery. It worked fine for a couple of years and all I ever did was check the battery voltage every now and then and made sure that charging light came on when the engine was running. When I dismantled the system a few months ago, I was pleased that both batteries were functioning well when I tested them, which was kind of surprising because I've ruined several of the Universal Battery products before.
The downside was that I wanted a bit more capacity and started thinking of putting my 150Ah AGM in the car instead. The big problem, though, was I wanted something smarter than the ISOpwr unit for charging the AGM, which seems to have done very well spending most of its life floating on a charger. I then started looking at ways to have the AGM battery hooked to a charger, which was constantly powered by the U1s, whether the vehicle was running or not, and continue to use the ISOpwr to charge the U1s when the engine was running.
I started another thread a few months ago to explore how to best go about this, and, thanks to TexasGirl and Carl, decided to use a PWRgate and a DC to DC step-up converter between the batteries. There are more details at:
http://thesurvivalpodcast.com/forum/index.php?topic=53164.0
Basically, the PWRgate is designed as a battery backup for ham radio operations, which charges the battery from a DC power supply and can instantly switch to the battery if the power supply goes down. It has a fairly sophisticated 3-stage charger and has a jumper setting for AGM charging, but it requires that the power supply voltage be 14.5V in order to reach peak voltage during the charge cycle. What I needed was a way to boost the voltage coming from the pair of U1 batteries and use that as the power supply input for the PWRgate. This led me to experimenting with an inexpensive unit from Amazon and building one into a case with Anderson Powerpole connectors that would join the ISOpwr and PWRgate units.
After I bench tested the various components (and blowing up my PWRgate, necessitating shipping it in for repairs), I had to figure out what kind of container I was going to use to hold everything in the back of my vehicle. I was torn between using another Pelican case or a rack mounted roadie case, but in the end went with something pretty mundane.
I've had this cheapo plastic four-drawer storage thingy for at least 12 years. As much as I'd like to get rid of it, I still wind up putting it back in because it's so useful, so I decided to put the batteries in the bottom drawer and everything else in the drawer just above it.
The batteries fit perfectly, but I did have to get a little creative with fusing all three batteries at the positive terminals. I wound up bolting the fuses directly to the terminals, instead of using the usual fuse holders for this type of fuse.
Next, I needed a way of organizing the inverter, ISOpwr, voltage booster, and PWRgate in the second shelf.
I found a perfectly sized piece of wire-shelf cutoff and discovered that I could wedge the ISOpwr and PWRgate units onto it to act as legs, hold them in place with zip ties, and have an inclined shelf that allows the inverter to breathe, as well as improves access to the switch and sockets. Plus, reading the status lights through the clear plastic drawer fronts is easy and can be done without having to pull out the drawer.
I used 2 gauge wire from the 150Ah battery directly to the inverter, and a fused 10 gauge wire from the PWRgate for charging. I set the maximum charge at 4A. The two U1 batteries were wired in parallel with 4 gauge wire and a 10 gauge connection to the ISOpwr. I duct taped a meter to the drawer front so I can check the voltage of the U1s and make sure they're not getting too low.
For the last 10 days everything's been working great. The PWRgate is getting the constant 14.5V it needs and the AGM battery is staying on float. The voltage on the U1s hasn't gotten below 12.3V and they're staying charged with just the short little bit of driving I do, even when I don't go anywhere for 3 or 4 days. The current overhead while in float is less than 100 mA, with half of that coming from the ISOpwr, which seems kind of high since it's not doing much when the vehicle is off, but that's still much lower than any of the other options I experimented with.
The next stage will be to add a RigRunner for DC power distribution, USB outlet, and NiMH charger.
