Smart Battery Follow-up

I thought it would be fun to hammer my battery today. I've got everything 12v turned on - refer on 12v, the tv, the stereo, the fantastic fan on high and every light on. We'll see how long she goes. I have the autostart on the generator set to come on at 12.1v - that should be deep I'd think. Any guesses how long to expect?

At 4 hours, I was at 12.1 volts and the generator started. From the chart on Smart Battery's site, that should be essentially empty, but I have no real way of telling. Interestingly, the gauge on my Onan remote was reading 12.1 volts, but the gauge I have in the cabin was reading 11.8. I think I can attribute that to the 12v pickup on the generator is a straight line to the battery, whereas the 12v outlet in the cabin has the block and fuse panel and wiring between it.

Anyways, I have some observations on charging. Firstly, the charger is running flat out - both fans spinning. Even though the spec is the same as my old charger (725 watts/45 amp) it must be putting out more of that because I popped my GFCI in the garage (running on a 15 amp drop cord). Could just be a coincidence, but the only time it's done that was with the AC and other things running and a long drop cord.

Secondly, the voltage showing on the gauge is not the same as I was seeing at the shop. When I first installed the battery, it was reading 14.5 volts. I now suspect that the battery was delivered fully charged and not the 30-40% charge I was led to believe. Now, with the depleted battery, the voltage in the cabin started at 13.2 and is rising. After 2 hours it's bouncing 13.8 to 14.0. So instead of the constant 14.5 this charger claims to put out, it either ramps up until it peaks when the battery is full, or it's just the method of how we are measuring the voltage, I don't know.

As I said before, I started this test with a hot refrigerator - above 80 degrees inside (it's quite hot here). So I suspect that it was needing 15 or more amps trying to cool down. It did get close to desired temps inside in the 4 hours, which was better than I was expecting. My fans, lights, tv's etc, must be using 4 or 5 amps. 1 light in the bathroom is incandescent, so it's probably 1 amp by itself. Same for the 2 fans. The TV and stereo are negligible. The CO detector is probably 1 amp. I have no idea on the LP system - the manual says to engage the cutoff switch when not in use to avoid draining the battery, so it must have some parasitic load.

I've been on the charger for almost 3 hours. I really expected to be fully charged by now, but I guess not. I'll report back when the voltage is back at 14.5. I don't think it needs to sit for any length of time when it reaches that point.

Even though the current voltage is reading 14.0 volts with the charger running, if you shut it off, the voltage reads 13.4 volts, which would indicate a full battery. But you have no way of knowing if it's truly full. Good thing with lithium is that it doesn't really matter - it is just fine to be partially charged.

OK, at 3.5 hours, the voltage is reading 14.5 volts. The charger is cool and the fans not blowing. So now I'm pretty sure that the battery is now full. But also, it doesn't appear it is putting anything into the battery, and could probably be just left online.

It just strikes me that it shouldn't work this way. But the charger may be putting out a constant voltage to the battery, but the 12v system in the coach is not reading it that way.

Update 7/26/15:

Today I re-ran the test with a few tweaks.

First, I left the RV plugged in over-nite. The refrigerator was cold to start with. Started at 13.4 volts.

Turned everything on again. I suspect the refer is now drawing less. Not a whole lot though.

I adjusted the setting for the Onan autostart to 11.9 volts.

I heard it come on after 5 hours. So that's an additional hour run time. I turned off the generator and started the engine.

After an hour of idling, if you shut down the engine, the system shows 13.2 volts. That's a bit short of the full charge 13.4. After two hours, it was reading 13.3, so I shut it off. Close enough.

Not sure if driving the van would do any better.