<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto">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. <div>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\u2019t get into detail here, but they are worth investigating, if you want details.</div><div>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 <i>cell</i> 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.</div><div>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\u2019t measure the individual cells within. </div><div>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</div><div>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. </div><div><br></div><div>Thanks, Daniel O. Duffield, NM EE98, NABCEP Certified PV Installation Professional. IEEE member.<br><div><br></div></div></body></html>