So, I’ve always tried to be careful about the bus batteries. Without them the bus really doesn’t move, which can be frustrating as you sit in your driveway ready to go somewhere, and really frightening if you’re at a site and it’s time to leave. I’ve run into both of these situations, and learned a lot from them.
One of the things I had learned was that the two batteries that our bus came with didn’t keep a charge long-term. When we first got it, and I discovered this, I went through the system with as fine a tooth comb as I could for the seeming miles of wiring looking for places where there could be a drain.
I ended up removing a tachograph which had a clock that kept running, and disconnecting a number of system from power, even though they were on a circuit that ran off the ignition switch triggered power relay, just in case. The one thing that I couldn’t detatch was the ECM, which draws some 700 mA to maintain the error codes and other brain-related functions.
In order to combat this small drain, I picked up a small solar panel to essentially be a trickle-charger and offset the ECM’s needs over the long periods of not being used. 
While this helped, I continually was having problems if the batteries were left alone, to the point where I’d throw them on the charger before I went anywhere if I hadn’t had a chance to start the bus in the last month. Overall, it wasn’t so bad. And after the bus had run for a bit, the batteries would be fine.
Once I installed the DC inverter and ran AC power in, I had thought things would get a little better. The inverter was supposed to not only change the AC power to DC, but also charge up the DC batteries. I had hooked it to the house batteries, but found after our fateful trip to Evangola State Park (when the alternator died, as did the bus batteries) that it wasn’t doing any charging.
Subsequently, I got a couple of battery-tenders for the battery sets. 
Unfortunately, due to a number of factors, I didn’t move the bus (or even try to start it) from October to April. It sat with the maintainer attached, so I wasn’t worried, but when I went to start it to go get it inspected, there wasn’t enough power in the batteries. A little annoyed, but otherwise un-phased, I got out the car charger, and sit it up to charge overnight. The next day, I went out to start it, expecting the batteries to be ready, as they usually were after a charging event like that, but they just barely got the engine going.
Usually after some driving time the alternator cranks out plenty of power to charge the batteries, and as I watched the voltmeter on the dash, I could see that the alternator was pushing out 14 volts (which is pretty high compared to the 13 or so I normally see), so I was sure the low batteries were getting what they needed.
So, it was a bit of a surprise to talk with the dealership on the phone (there were some issues with the suspension system in order to pass inspection) and find out that the batteries were dead when they went to bring it into the garage for the inspection. They asked if I wanted them to deal with the batteries, and I said no. So long as they could give me a jump to get the bus back home, I’d deal with it.
One of the big reasons for this is that if there’s a short somewhere that’s causing the drain, it could rack up some serious dealership-level mechanic’s hours in fees. And it’s something that I could trace and deal with on my own. I was also sure that nothing was an unnecessary parasitic draw (the radio, for example, runs off the house batteries, so even the electricity for the memory for the preset stations doesn’t drain the bus batteries), and I didn’t want to have mechanic time going to check that.
So, I started in on testing …
(Continued in Part II)