House Battery Testers

[mikestead]

My SMB doesn't have any instrumentation to show the charge status of the house battery. Being an electrical idiot, does anyone have a recommendation for an inexpensive but reliable gadget for this purpose?

We are boondocking in a couple weeks for the first time, and I'm a little uneasy with one house battery for the 4cf fridge and possible overusage of interior lights and such. And possible short episodes of the microwave (will need to get an inline inverter for this).

I would like to be able to push a button or stick something in a 12v house battery outlet from time-to-time that would tell me how much charge has been used up.

Thanks,

Mike

[Jeffrey]

I thought that all SMB's ship with a cig lighter plugin type of voltage/battery tester... Mine did.

[sdwindansea]

Mike's SMB is a 1995 so I'm guessing it has been lost or was built before this became a standard option. Jeffrey is correct that all SMB's now come with a voltage meter that just plugs into the cigarette lighter operated by the house battery. It seems really accurate since it always matches my Blue Sky controller within a 0.1 measurement. I'm guessing this is a really inexpensive item and you can always contact SMB to get one through them.

[jage]

Yeah they're pretty cheap. Mine goes red yellow green with lights.

[mikestead]

Sounds like what I'm looking for. . .cheap and SMB-approved. What brand is the one supplied by SMB? Any other markings? Maybe a picture?

[Ford_6L_E350]

I have an extra one I'll give you for Christmas. Just pay the shipping - about a buck.

Mike

[mikestead]

Hey Mike, that's very generous of you. I appreciate that. I'll PM you.

A Merry Christmas to you and the Sportsmobileforum gang as well. This used SMB my wife and I bought last week. . .I really do feel like a little kid at Christmas.

"Alaska to Key West". . . .The boondocking I mentioned above is stealth camping in the Keys for a week in February. Do a little beach, a little fishing. a little tiki bar. Pidgeon Key Art Festival. Kick around Key West. My wife Vicki and I lived in Marathon in the middle Keys for 3 years working at the hospital there. It'll be like old times.

Happy Holidays, Everyone.

Mike

[daveb]

Mike, how much do you want to spend? I just upgraded my Mark IV solar controller for a new blue sky unit. The mark IV controller had LED lights that showed the status. I found the batteries usually would float back up depending on load, so the gauge was...well not real acurate but better than nothing. SMB says to follow the voltage, so a good (highly acurate) volt meter might work out. I have battery "fuel" gauges on my bass boat but really they are volt meters the measure DC voltage between 10 and 15 volts which point to red yellow and green. Batteries always float back up after a heavy load is turned off so its kind of hard to actually determine their status unless you know your system. Xantrex makes a good battery monitor called the "Xantrex Battery Monitor". I have a "Link-10" but it's somewhat complicated, in other words, I need a dummy book to run it. When I couldn't grasp how it worked I asked for the manual. It's over 75 pages. Check out Badger's web site. They put in the XBM but I really don't know much about it other than it's much cheaper (and less complicated) than the Link-10. Somebody put a good link to understanding batteries but not sure it's on this site or the owners group. I should add that there is nothing wrong with the tester that SMB provided me but the key is knowing how load affects the batteries and how much you have pulled out over a given period. Just because it shows yellow at 10PM after running your lights doesn't mean your batteries will be dead toward morning. Most of the time my batteries will float up even while running my Espar heater all night provided I don't apply an outragous load.
Good luck.
Dave Boyer

[mikestead]

Having just browsed some of this stuff on the internet, I see what you mean about "how much do you want to spend". That Xantrex monitor is over 250 bucks! I think I'll take baby steps on this issue, and start with Mike's offer. Perhaps a more sophisticated version in the future if I upgrade to a newer SMB.

Previously I saved the link to that long article about house batteries. I'll read it this weekend. Thanks for the reminder.

Mike

[scatter]

Mike - You're jumping into a long subject here with lots of opinions and answers. The plug in meter that some of us got from SMB will give you a good indication of whats going on with your battery. As was mentioned above, what you have plugged in at the time and when you check the voltage will greatly effect the reading. The table below is the generally accepted standard of battery makers.

State of Charge 12 Volt battery
100% 12.7 Volts
90% 12.5
80% 12.42
70% 12.32
60% 12.20
50% 12.06
40% 11.9
30% 11.75
20% 11.58
10% 11.31
0% 10.5

The problem is that it is only accurate when the battery has been sitting, and not being used or charged, for a minimum of a half hour with an hour being best. Kind of hard to find that scenario when on the road. If your battery has been charging and you check it, you might get a reading of over fourteen volts and that's a false reading that will drop off as soon as you stop charging. Same with when you have something plugged in. Especially a big user like a microwave. You check when the micro is running and you might see something like 11.5 volts, but let the battery sit and it could come back up to 12.5 volts. So, just use a little common sense when reading and try for a non-use time. Nice thing is that even if you draw down the house battery, you can still start the rig and charge it back up. Try and not do that too often though, it's hard on the battery and will shorten its life. If your battery is in good shape you should be fine with your fridge and house lights. Micro is another issue. Try it and see what happens. You might try it all in your driveway. If it works, you're good to go. If you draw the battery down too much, charge it up and back off on the power useage when camping.
A good check all of us can do when we suspect our battery is starting to go bad is do a load test. Probably best to have it done at a battery shop as our house AGMs will need a pretty big load tester to check 'em. A load test will tell you right away when a battery is starting to go. Not a bad thing to check on any battery over four years old.
Anyway, sorry for such a long post, batteries are simple, yet complicated and it's a bummer to have one go bad on the road.
Have a great trip, always wanted to do that one myself!!