Worst of all, the true value of the battery in the transaction may never be accounted for accurately. An excellent battery disguised by a poor appearance (that invites low pricing) may not earn the seller a fraction of its worth, or a cosmetically attractive, high-priced used battery may fail miserably at satisfying the user’s needs–spoiling prospects for future purchases by that customer. Such are the typical results of inattention to accurate battery testing and evaluation. One can learn a lot from a thorough battery evaluation, and the key word here is thorough. Distrust any spot check with a voltmeter or hydrometer that involves less than hours of battery equalize charging followed by hours of load testing under controlled conditions. The evaluation does not need to be expensive, not at all. It just needs to be thorough. An established battery service shop can provide you with a professional battery evaluation, one that really does include more than the compiling of a table of voltages known as a "test sheet".
The cell voltages that make up the test sheet do tell a story, but it’s a story that must be interpreted with the help of other information gathered by a technician with years of battery experience. He can tell you not only how old the battery is, based on manufacturer’s date codes, but he can tell you how big a reliability factor this age might be at this point in the battery’s life, taking into consideration:
Brand name reliability vs. age (track record)
Signs of abuse: indications of overheating, poor watering practices, etc.
Indications of impending failure of cell components
The voltage behavior revealed by a 6-hr. capacity discharge test
You need to know the above to know what to do next. Limited repairs, major rebuilding? If one cell has failed, are more to follow soon? An educated guess based on the evaluation can help you decide the most cost effective approach to battery repair as well as allow you to determine a fair resale price.
The Capacity Discharge Test
To get a solid idea about the condition of a lead-acid battery, one needs to do more than look briefly at voltages or hydrometer readings. For purposes of evaluation, the only meaningful voltage readings one can get from a lead-acid battery are those taken under rated load at a known point in the nominal run time curve. Controlled conditions are necessary to do this. In the battery shop, an adjustable load test resistance bank, a "load bank", is used to provide a constant-current draw for the entire industry standard 6-hour discharge cycle. Ultimately, the capacity discharge test allows the evaluator to tell the user a percentage (of nominal capacity) figure, and provides a basis for predictions about future prospects for the battery when other considerations are factored in (see above).
Look at the Big Picture
Clearly the value of a battery depends on the needs of the user as well as the absolute capabilities of the battery itself. A "good-running used battery" for one application, say a small machine shop with very limited lift truck use, might be totally useless for a fast moving food warehouse with high stacking and freezer operations. The difference may be as much as 8 hr. running time each month vs. 8 hr. of use each day. Many low-utilization applications are satisfied with a big old battery, one that would be over-sized for the user’s needs if it were new. And the charger used may be less than recommended size as well. But because the business has few and infrequent tasks for the lift truck, the battery has enough remaining capacity in its bulk to serve without complaints for years beyond the date it would have been removed from the line-up of a busy terminal.
The Used Battery Tune-up
A battery sent in for a complete evaluation will come out in the best shape it’s been in a long time. Why? In preparation for the 6-hr capacity discharge test, the battery must receive a long and thorough equalizing charge. This charging, aimed at bringing each of the battery’s cells up to an identical state of charge, also helps remove all traces of sulfation from the plates. This may involve days of carefully monitored charging on special equipment. Preparation for the test also includes adjustment of electrolyte (acid) strength to proper levels in all cells– an important factor in getting the most running time out of the battery. Corroded, high-resistance connections (cell connector straps, posts, cables) are also corrected for the test. Consequently, even if the evaluation does not lead to any further work on the battery, the battery will be in the best condition it can be when it comes out of the battery shop.
For more information, contact Arcon Equipment Inc. (440) 232-1422.