Quote:
Originally Posted by jage
Ok, so how does one determine the state of one's house battery(ies)?
Is it bad to kill the house battery? How many times?
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Am sure many will add to this, but the following is certainly true:
A. If you have solar or are pre-wired, you'll have a "fuel gauge" and a voltage read-out that you can use. Eric B. may chime in here: he didn't think the one that SMB used was that accurate, but it's not too bad. Read on his site at badgertrek.com; he also points out important things like temp effects, etc. Also, if you don't prewire for solar, SMB gave me a cig socket plug that read voltage also or you can buy one for ~$20; you just need to know how voltage relates to capacity (and yes, there is a temp effect).
B. It's REALLY REALLY bad for your batteries to run them down. Yeah, I know, they're called "deep cycle" marine batteries, but that doesn't mean that they like it. I haven't figured out how to upload files at this site, but have uploaded a "depth of discharge" vs. cycle life for various battery chemistries over at:
http://autos.groups.yahoo.com/group/spo ... ers/files/
The file is called "BatteryCycleLife_NREL.pdf "
"Depth of discharge" aka "DOD," is how far you run your battery down. Thus, 80% DOD is leaving only 20% left in it. As you can see, as you go to greater and greater DODs with an AGM battery, you _severely_ limit the number of cycles you get; doing 100% DOD will get you all of around 100 cycles.
To answer the question this will raise: what does that graph mean for end of life? What happens at 100% DOD after ~100 cycles? The definition is that now you only have 80% of the battery capacity that you had initially. Thus, your battery isn't dead or useless per se, but it's delivering far less total Wh than it used to.
If you send me an email address, I can email you the file (it's a PDF), and you can post it somewhere.
All of this is a strong argument for solar panels if you're going to go on long trips without driving much. Your batteries will just last a lot longer.