The tester for battery banks I have used for many years is somewhat pricey, but well worth it, since reserve battery banks are the single item in most stand-alone that are most difficult to quantify and now storage is finding is inevitable way into grid connected PV systems. The unit I would recommend is called, Mid-Tronics CTU 6000 Celltron Ultra stationary battery tester. This unit was first introduced to me, when I travelled around New Mexico and serviced Mitsubishi (zero transfer time) 3 phase Uninterruptible Power Supplies, powered by either 30 - 12 volt batteries wired in series or 40. These are lethal dc voltages, but these unit also work on 12, 24 or 48 system. These units perform something like an impedance test, actually a conductance test - mhos. They record data sets on an SD card and you can immediately print out the results on site. I have used these to test hundreds of GNB-Absolyte VRLA AGM batteries over the years. The have other benefits- which I won’t get into detail here, but they are worth investigating, if you want details. I took my time and found a good unit, at a decent price on eBay from a re-seller with a good feedback rating. They come with some of the major battery type reference cell values within the unit for comparison of you can add a value yourself after consulting the specific battery type your testing from the mfg. The only limitation is - this is a cell tester and when testing you need physical access to the individual cells to place the testing probes upon. Most large amp-hour banks are made up of as few parallel strings as possible- which leads battery designers to produce batteries with progressively large amp- hour 2volt cells, whose terminals are directly accessible via bus work. If you have a 6 volt/12 volt building block, like a L-16 or a 12-volt group 30 footprint type battery- you can’t measure the individual cells within. If you have a very large number of banks to test, you place your probes on the 2 volt cell terminals and wait for an audible beep, prior to moving on to the next successive cell in your string. In this manner you and be accurate and fast These work very well at finding issues and indicating how relatively close or far away the measured conductance value is from a known good value.
Thanks, Daniel O. Duffield, NM EE98, NABCEP Certified PV Installation Professional. IEEE member.
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