Off grid, running generator to charge batteries

Thanks! Have been leaning that way all ready, but didn't know the reason, now I do.

Well this is an easy question... don't use that 12v "battery charging" port on the Honda for anything (except an emergency). It's the only poor feature on an EU2000, just pretend it doesn't exist.
It's unregulated and will overcharge and cook your battery... eventually. It's also not very powerful.

Got my curiosity going, which is better? I have a Honda EU2000i, It has a 12vdc battery charge option (along with the Honda cable) to hook directly to the batteries. I usually just plug in my 110 vac shore cable into the generator to charge for a couple hours (2-4) during the day when off the grid. That seems to be the best, but have never really tested one method over the other. I only have the factory "idiot light" indicator for charge level, and 2 lead acid "RV" deep cycle battery bank for house batteries.

I do carry an extra "RV" marine battery in truck bed for my 110 inverter/AC use when "off the grid". This way I never really have to worry about draining the "house batteries" for non-essentials. It is not wired into the "house" system - but has been on the "to-do" list for a long time.

Having said that, I grew up in and around sail boats which for years only had the the single motor starting battery for electricity, so conserving power was taught at a very young age! All the power options we have are in the TC are "luxury" compared to those days.

So is it better to use the "house" charging system when off the grid, or the Honda's 12 vdc option?

BTW - this feels like a "dumb question", but always just kind of wondered. My "system" has worked for yrs. First set of batteries lasted 9 years this way. The truck bed battery doesn't make it that long, but that gets swapped out of the boat from time to time to rotate and always have the best battery in the boat....hard to walk back to the camp site from the middle of the lake!

Charge rate slows the closer you get to a full charge. That is by design to prevent an overcharge. The end result is you will get little benefit if you charge for several hours if the battery is near full after being on charge for a while.

I don't worry about keeping a "full" charge. Instead, I run the generator a short time to make sure I don't go to near empty at night. BTW, 87% was already close enough to full to need only a few minutes or at most an hour. That being said, I just use the 4 led lights, so I don't have a percentage to compare to yours.

towpro wrote:
we are supposed to be going to beach off grid this weekend for 5 days (they are calling for rain showers, clouds and maybe thunderstorms for 4 of those 5 days). Generator is packed.

You coming down to Assateague?

This is the problem with lead acid battery technology. The acceptance rate tapers dramatically as you get above 70 or 80 percent state of charge. On boats where batteries are the only power, you run them down to 50 percent and charge to 80 percent. That is the sweet spot. The problem is that with AGMs you need to charge to 100 percent periodically (perhaps once a week) or they will die young.

This is also why all the hype about LiFePo4 batteries. They will take a very high rate of charge right to the top. You do pay a price for the capability.

Hi Towpro,

I would not have started the generator at 87% state of charge. Best bang for the buck is from 50% to 85% (or perhaps 90% with AGM). At 85% charging is limited to about 12.5 amps per 100 amp-hours of storage.

Fastest charging is to come close to the gassing voltage but NOT exceed it. Temperature compensating charging is the way to go.

If an AGM bank is accepting 0.5 amps per 100 amps of storage capacity it is de facto fully charged.

In my case i gave up and all of those P1 L1 C1 PDQ numbers along time ago... I just know what I need to be doing to make it through the day/night run on my 255AH battery bank so I can use my generator the next morning at 8AM for three hours to get me back up to a point where I know i can do all of this all over again for the next day/night run on my battery bank... I also know I can do this setup for ten or eleven days and get almost the same result every day... After 10 days of doing this then my performance starts falling back and each day I keep going it starts getting to the 12.0V (appx 50% point) earlier and earlier each evening.... Then I have to stop everything and do a slow good 12 hour smart mode charge and things then jump back to their normal life again...

I am hoping to add some solar panel this upcoming season and this will just be icing on the cake as for as I am concerned. My routine will be almost the same as before except I may be able to cut back on my generator run time to one hour verses three hours. Once my batteries are accepting 6-8AMPS DC current then I can allow my couple of 100 WATT solar panels do this during the high sun day . However if for some reason it is not going to get me back to at least the so called 90% charge state before lets says 4PM each day then I will run the generator again for a couple of hours... My converter/charger will be producing 13.6VDC during this two hour run... I know from experience if I don't start with the 50% charge state then it shuts me down around 10PM at night and I have to disconnect the battery bank until 8AM the next morning when I am allowed to run my generator again.

These are the pitfalls I run into camping off-grid. Not so much getting all of those numbers you are talking but knowing what to expect from the battery performance during the evening... My savings grace is I have a good DC VOLT METER and DC CURRENT METER setup reading both Negative and Positive DC Current depending if I am in charge mode of high current drain mode...

actually it is all pretty much normal runs now since I have been doing this since 2009 with this particular battery bank setup. When I get my newer battery bank going i will have to develop my Battery bank standards all over again on what will work and what won't...

I already know of one pitfall coming up is my PD9260C only produces 14.4VDC boost mode and the GC2 6V batteries I am going to be using want to see 14.8VDC. I have been figuring it will be just fine using the 14.4VDC but will take a hour or so longer to meet my marks... I probably will be getting a different converter/charger before it is all said and done with haha... Randy at Best Converters sells a PD9260-14.8 model now...

My generator is my savings grace and if I had solar it would just be icing on the cake...

Roy Ken

towpro wrote:
(they are calling for rain showers, clouds and maybe thunderstorms for 4 of those 5 days).

Sounds lovely.

Thanks for the info everyone.


all my measurements are done on battery shunt (that is where 2030-RV is wired)

After typing the above message I turned off camper charger and Solar system than put AGM battery charge to it. within an hour it showed 100% on charger.
Next I reset Bogart back to 100% (showed 96%) and turned solar back on.
I know its still charging because it was accepting 1.7amp from solar.

I have Bogart Trimeter plus solar controller
I have program P7 sett to L4. I think over time without sun this full charge number gets harder and harder to reach.

below from Bogart manual.
There are two different standards you can select to define a “full charge.”
The highest (more stringent) standard is selected by using TM-2030 program P7 to choose L4 instead of L1, L2, or L3
which use a lower standard, which requires only that the battery voltage exceed the value in P1, and that the charging
amps be less than P2. The L4 level requires that in addition either the required "absorb time" or "percent overcharge"
be achieved, such that the "float" state has been reached. This establishes a better, but more difficult, level to reach.
Refer to the TM-2030 User's Instructions, section 6.2 for details.

we are supposed to be going to beach off grid this weekend for 5 days (they are calling for rain showers, clouds and maybe thunderstorms for 4 of those 5 days). Generator is packed.