House Battery Won't Hold Charge But...

[Viva]

Hi E277,

Glad I didn't overwhelm or annoy

I understand wanting to keep it simple on an older van (although my buddy's that we did is a '97, but I still get what you mean).

If you changed to a larger wire running back from the separator to the house battery (did you?) that is good. The one on my buddy's (my former) (Indiana) '97 is something like #8 - WAY too small. Voltage drop city. Changing that to a larger cable (which you can then even fuse for safety if you want to) will help get more voltage back from the alternator. That said, the alternator is still not a smart charger. Still, why waste what you can get from it.

Do you tend to do weekend trips only? If so, consider this for minimal outlay and complication (I will ignore proper fusing and etc. for the time being, since you aren't looking at a system overhaul, and this would not be making anything worse).

1) New house battery, so you know where you stand. If keeping the SMB "venting system," and the battery is under the couch (mine was), consider AGM for fewer venting concerns. Of course this goes against "cheap." So maybe keep flooded cell batteries....

2) If you can swing it, a second house battery (I added this, under the couch). This will double your available power over a weekend.

3) Now just plan on putting the power back when you get home, via plugging in/charger. If you can, put in a smart charger (will be much kinder to batteries, plus charge up to 100% much better). If you are going to be plugged in for a period of time (days), then you don't need a large one (smaller one takes longer). Maybe say something like this, which is a smart charger, but smaller amperage (I have a larger version of same in my current rig):

http://www.amazon.com/ProMariner-63120- ... ic+charger

It may be cheaper elsewhere.

(Note that I am not a charger expert, as plugging in is not my usual way, but these are well-rated by folks I trust in the marine industry.)

AGM's CAN take charge really fast, so with a generator (or short plug in times) you can really make good use of a larger (60 amp say) charger (who wants to listen to generator drone on and on). But if you are plugging in at home, then I don't see any reason 20 amps can't work fine. The "smart" charging is really helpful for treating the batteries well, plus getting that last 15% in. Lead-acid atteries generally don't like being charged up to only, say, 85% over and over (lithium is different, but we're not going there now).

If you are going the "cheap and replace" route, plus with predicatably short outings, then maybe don't spend for a monitor (I can't believe I'm saying that, LOL), but instead do some manual calculations. Say like this:

One weekend:

1) Furnace fan, amps x hours used.
2) Lights, amps x hours used.
3) Refrigerator (maybe not possible - do you use a cooler?)
4) Laptop charging (a 12 volt charger is better than using inverter plus 110 charger), amps x hours used.

etc. etc.

If you can put in enough amp hours in the battery bank so that the figures all add up to less than, say 75% of your amp hours (normally I'd say 50%, but you are going for cheap/replace theory on batteries), then you can just go about your business and then plug in for the week to re-charge, then repeat the next weekend.

Here is a chart for Lifeline batteries, for example, comparing percent of discharge vs. cycle life. You can see that 75% discharged will still work, especially in an "I know I'm going to kill these and then replace" scenario.

Hmm, not sure I remember how to get an image from my album to a post? I put the chart image in my album at any rate.

[xcnick]

I can't answer as well as Viva, but I share your pain. He helped me in the thread viewtopic.php?f=14&t=15667&start=30

On page 3 I show pictures of a battery box for two 27 batteries under the seat. This was the cheapest way to get the capacity I needed.

What we missed is what Dave said. One can not use the entire battery. We need to only use half the battery so basically we need two batteries to do the job we initially thought we could get out of only one battery.

I have had many test my van battery and many of my car batteries and tell me to replace them. I still get another 3 or 4 years out of them after they tell me it bad. I have my own load tester and often they test well at home even though the "pros" tell me they tested it as bad on theirs.

Try to recover the coach battery you have charging at home. Check how you are charging. If I use the van plugged in, my van charger (Power Source PC-45) is set at only 13.1 volts. therefore it is better at just keeping it charged . If I want to fully charge it I use a separate charger pluged into the wall to bring it up above 14 volts.

[xcnick]

And I also have a coach battery I know only last 1/3 the time but passes the load test. This may be true of only Marine type batteries which also start a motor. My thought is true deep cycle batteries would fail the load test even when new. The load test simulates a starter run for 10 seconds while watching the voltage drop.

[E350]

Hey guys, do you have a recommendation for a specific make and model of 110v smart charger? Something that when I get home and I want to recharge or maintain my AGM (or potentially eventually Lithium) house battery of say 250AHr or larger, say 400AHr. Or to use when I get to an rv park or have other shore power available so I can plug in and charge?

[boywonder]

Originally Posted by E277

I do not have a "smart" charger; however, why would you have to disconnect from power after an hour. What about when you are near hookups and plug in for the weekend for instance. I simply plug the 30 amp in the side of the van and flip all 4 of the breakers in the van. Is that harming things?

Is the charger that you are referring to the one built into the van by SMB? Is it an intellipower brand converter/charger?

Also is there any chance that you can post the brand/model of your isolator?

The reason to be a little gun-shy with a non-smart charger is that there is a potential to overcharge a battery. Sounds like it may not be a big concern for you if you are buying reasonably priced wet-cells. Folks get nervous with $400 AGM deep cycles.

If you limit the charge time you reduce the risk of overcharging/overheating the battery. Once a battery is fully charged and the charger keeps charging, the battery temp rises, and will boil off electrolyte if it's a wet cell and possibly vent a sealed battery; both of these conditions are bad for the battery.

If you do leave your charger on overnight, see if the battery is warm/hot in the morning.....