batteries :: what I’ve learned

3.20.2012 – Tuesday

I wouldn’t say that I love to research a topic but I have a tendency to disconnect from reality for a time while I focus on finding the answer to a burning question or some topic of intense interest. After more time than I’d like to recount, I’ve collected my own notes on flooded lead acid batteries (FLAs) and compiled them into a spreadsheet. WordPress isn’t the friendliest when it comes to handling spreadsheets so I converted everything over to a JPG for the sake of preserving my formatting.

Here is the PDF version of my FLA notes (printer friendly).

3 thoughts on “batteries :: what I’ve learned

  1. offgridcabin Post author

    Thanks for posting the link! I focussed this post rather narrowly on the terminology that I hear when reading through battery manuels, forums, and even scientific literature. Looking back on the post I probably didn’t need to include some information: like citation #17 – I looked that up because I was trying rule out the effects on gas solubility in water affecting my specific gravity measurements (turns out charge lag was to blame at the time).

    I filed the linked article in my off-grid folder on my computer. It’s well written, simple, and clear – a rare balance to strike with technical writing. Thanks again!

  2. Jonathan

    Thanks for sharing this information.
    Something I learned recently might be of interest to you. I met a man who has 40+ years experience in the USA with off-grid solar. His business was one of the first doing off-grid solar in a big way.
    He mentioned that it is best to not have any batteries in parallel. He said putting them in parallel has a number of significant disadvantages:
    – The batteries will develop internal resistance, to differing levels. This will result in unequal resistance over time, which will result in uneven charging and discharging, which will wear the batteries (reduce their life span)
    – For the same reason as above, it is not a wise option to replace any one battery. The new battery will have completely different resistance to the old ones, and will die prematurely. Thus in a parallel setup all batteries in the same parallel bank will need to be replaced at once.

    His advice was to do everything with 2V batteries, in series. For most situations he advises a 24v bank, which means 12x 12V batteries in series. With an MMP charge controller one would set the panels up to feed in at roughly twice the storage voltage. So in this case that would be around 48v. That’s not exact though. For instance, I have 8x 130w Kyocera panels. They produce about 16 volts with full sun. Based on this guys recommendations it would be best to set up those panels in either 2x parallel banks of 4 panels in series (giving around 60v) or 4x parallel banks of 2 panels (providing aprox 30v). The advantage of the higher voltage is greater effeciency, longer cable runs, with smaller wire.

    Normally we put batteries into parallel to get the storage capacity one needs. Using 2V batteries it is possible to buy batteries in a wide range of capacity, up to VERY large sizes. He said that for practical purposes an 1800amp hour battery is about the biggest one can use (for two people to lift). The other advantage of 2v batteries, according to him, is that you end up with large cells, as opposed to lots of little cells. As you no doubt know, a 12v battery is made up of 6x 2v cells which are roughly 1/6 the physical size of the 12v battery. In a 2v battery you have one large cell. He said that these large cells last much longer than the small cells.

    He said that he has been running his off-grid house on the same bank of 2v batteries for 19 years so far.

    I thought you might find this information interesting.




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