Originally Posted by sapo
hopefully this is related enough not to be off topic. I'm buying new batteries for my solar-charged house bank. I'm told that one should test the batteries at the store to make sure you're not being sold old stock or otherwise batteries that are otherwise less than optimum. but how do you test 'em? just with a hydrometer?
You can just measure the open circuit voltage with a volt meter. There is no real benefit to measuring the SG on new batteries because the cells are still new and un-cycled...
They should be above 12.6V or darn close to it. Try to buy batteries with matching date codes and the freshest date codes on the shelf. For example if there are four group 31 batteries and you need two, and the date codes look like this:
You want the two J12 date coded batteries. they theoretically should match better and have been produced at or about the same time. Often times the letter is the month with Jan being "A" and the year being "12"... This may not be the same for all batteries so ask your supplier how to interpret the date codes and choose the freshest batteries..