question

@Allswell

Well, after 10 years of full-time sailboat cruising, and another 10 years full-time in a motorhome -- I have a few thoughts on batteries. :-)

First, when it comes to flooded, gel and agm batteries and charging by generator -- living between about 50% and 85% charged is where you'll end up. This allows you to bulk charge the entire time you're running your genset, giving you maximum output for the fewest generator hours.

With these battery technologies, it just takes too many additional hours to get your batteries to float. Temperature is also a factor in battery performance, and since you get little light this time of year, I suspect it's cold there too -- with the corresponding fall-off in battery performance.

The equation changes when you have solar available of course, as getting to float is generally a daily goal. Lithium-ion changes the situation too, as you can bulk charge most of the way to 100% with a genset.

So I don't think you're doing anything wrong per se. However, I think you'll find this time of year you'd be better off with more frequent, shorter generator runs. Bulk charging and the early part of the Absorption cycle are the most productive. You will want to charge all the way to Float occasionally, but if you're like me that'll happen when you have other needs to run the generator.

@Allswell

Not a long enough Absorption charge means the chemical reaction is not fully reversed to get to the true 100% SOC.

We ran on lead acids for over five years... Killed the first set with bad practices such as not fully charging every day (and the real full charge, including a good absorption phase).

Lead based batteries do not last long being kept in partial states of charge. You might benefit from reading this book. Wish we had it when we first started.

@Allswell @Alexandra

Everybody's situation and use case is a bit different, but in our case anyway, the amount of time and fuel it would have taken to get our 800Ah battery bank to Float everyday would have been prohibitive. When under sail, out on the open ocean, maybe a 3 or 4 hour generator run would have been OK. But at anchor, I doubt we would have been very popular with our neighbors.

We found, that for us, a couple of 45 minute generator runs at the beginning and end of the day worked best. We could pull of fridge and freezer holding plates down, make water at 25 gph, and put 100Ah or so back into our batteries with each run.

We replaced the gell cell batteries the original owners of our boat had installed with exactly the same batteries after 2 years, and got 8 more years out of the new ones before we sold the boat -- and it wasn't like they needed to be replaced immediately at that point.

I appreciate that some books, and manufacturers may say different, but we found that those sources often fell short for those of us really putting this stuff to the test.

+1 for @Alexandra comments about partial charging.

Some thoughts.

What's your ac input current limit set to? Could be you're limiting the generator input to the batteries. Certainly the multi isn't capable of pumping all the generator output into the batteries, this will waste fuel.

Your charge efficiency seems high, Probably more like 90 or 85% would be more appropriate.

Charged voltage/absorption voltage seem high, what are the battery specs?

What C rating is the battery capacity stated? If you have shorter periods of heavy current, this will reduce the effective battery capacity. But from your load description, doesn't look likely.

What are temperatures in the battery housing? Lead capacity falls a lot with low temps. The battery data sheet will, if you're lucky, have a factor for capacity change with temperature. Guessing this is the cause. But worth checking the rest.

@Allswell

Don't get me wrong -- I'm not saying there's anything wrong with getting your batteries to Float. It's desirable, and is very doable in a solar panel and Lithium-ion battery oriented world.

Having said that, when you're dealing with more "traditional" chemistry batteries and a generator, long charging runs have multiple things against them. Noise, inefficient fossil fuel usage and increased maintenance just to name a few.

I agree with @kevgermany that your charge efficiency and absorption numbers seem high but I don't think either are going to be the magic answer.

As I said before, I think you're battling cold conditions for your batteries along with trying to get them to Float. Trying to get that last 15-20% into your batteries can and will increase your generator run times and fuel usage by a multiple.

How about adding a wind generator or two into the equation? I'm guessing you have some wind? Yes, there's some noise, but it might be just the ticket during your long dark winters. Bulk charge with the genset and let Mother Nature get you to Float. :-)

@Allswell

After looking at your profile, and assuming you're still roughly near Vancouver, I have a couple of additional thoughts:

At 50 degrees N more-or-less, you should be getting some production from your panels. This assumes decent placement, and angle for Winter solar. And as such, the time of day you run your genset becomes important.

Ideally, you want your more limited Winter panel production to address the gap between the efficiency of Bulk charging and inefficiency of later in the Absorption cycle -- while at the same time unlocking that battery capacity between 85% and 100% charged. Best for your batteries, as others have pointed out, and better for you to go into the evening starting with a full charge.

I think you'll find, as we did, this means running your generator first thing in the AM. Get that bulk charging done before the sun starts contributing. And then, let your more limited panel output contribute when your lead-acid batteries can't take as much amperage anyway, in the later stages of the Absorption charging phase.

A wind generator could help your cause too, but given your latitude, it seems like your panels should be able to do the job when properly combined with your generator.