House battery not charging when engine is running.

[kdarling]

I was amazed at the vagueness with which many AGM battery makers describe the minimum safety ventilation. For instance, your battery docs only warn against being somewhere with “minimal airflow”.

It took many days of searching before finding a few safety lab tests where it worked out that basically for about each 100Ah set, you need a 3-5 square inch vent both top and bottom, just in case. Say, 4x1” each, or 2” diameter circles.

The typical Chinook couch or sink cabinet would seem to have plenty of airflow around its edges. Under my dinette seat would not, thus it’ll need some vents.

I mention this because many people have gotten the impression that AGM need no ventilation at all, and that’s not true.

[Blue~Go]

Yes, I've gotten off easy in terms of needing to calculate because the under-couch space is pretty well ventilated (and easy to make moreso), and also cool as a cucumber in most circumstances. Also, since I primarily charge by solar, my batteries are typically charging when they are at their coolest temperature (for example today at noon it was something like 69ºF outdoors, the solar controller (also under the couch and right by the batteries) was at 57ºF, and the batteries (being charged at 14+ volts in the absorption stage) were at 46ºF (why I like temperature compensation for lead-acid batteries). By the time the batteries would even be close to coming up to ambient temperature, the sun's probably gone down. Not that I'd foresee any problems charging at any time of day or night, but just an added "bonus" with solar and a massive bank of lead.

Also, my battery "box" only has two sides and a top - the remaining two sides are mostly open.

[tjmackle]

This may help. When I found out my 1998 Concourse was only putting 10 volts into the coach batteries,
I was advised to check both sides of the battery splitter. It turns out that the battery splitter (located on the left side of the engine near the left headlight area) was charging the chassi side OK at 14 volts but only 10" volts went to the coach battery side. This splitter came with the original 1998 manufacture date which puts it at 20 years old. There was corrosion all over the unit which made it obvious it needed to be replaced. The name of the manufacturing company is on the unit (sorry, I didn't write it down) as well as the part number so all you have to do is Google the company name and you are there. The old part numbers are almost the same other that the new part has -A at the end. Could not se one bit of difference including the mounting bracket. I've noticed some owners have stated they have tried battery splitters from other companies for a varity of reasons. Sticking with the original company will solve the problem.
From this event, I learned that this problem was why the battery start assist switch never worked for me because it needs 13.8 volts from the coach battery side. After replacing the splitter, its back on line.
And remember, if your chassi battery is competely dead at 0 Volts this feature will not work. (4 volts required)
TJ Mackle