This is a very good article and touches on most issues and just to add my 1 ½ cents worth, here are a few things that come to mind. We all know that the best way to avoid a failure is to change the battery string before end of life. With the tight budgets and relative high cost of batteries, most data center managers want to get all they can out of each battery string. There is a fine line between getting all of the life from your batteries and putting your facility at risk. There are a few things that can be done to limit that risk. Depending on how critical the customer views their uptime, the preventative maintenance activity can be increased to quarterly or every other month. I would personally recommend installing and testing a battery monitoring system. A battery monitoring system will allow you to establish a base line of the battery strings and trend the batteries as they age. This will allow the user to get the most from each battery string.
The author, Brian Loken, mentioned something that I always knew, but is not really discussed. Loken made the statement that storing the batteries at 50F degrees will increase the life of the battery. This is totally true and if you want your flashlight batteries to last a long time store them in the freezer. If any of you have done this you know that when the batteries are first reinstalled in the flashlight the beam will be dim until the batteries warm up. UPS batteries are the same way; this proves the fact that UPS batteries will lose capacity when the UPS room is too cold. However with that being said, we have seen this actually increase the facility’s reliability. I know that’s a bold statement but let me explain. Several years ago we saw a high failure rate on a particular type and size of batteries. The failure rate was as high as 15% to 25% of the string per year, and many of them were open cell failures. One job site had this exact type and size of batteries seeing this type of failure rate. The very small UPS room is configured in a manner that the CRAC discharges air directly at the UPS and battery cabinets. Every time we would service the batteries; they were flagged between 62F to 65F. We discussed this issue with the customer and let them know there really wasn’t anything that could be done with their current configuration, and the only real impact was that they were going to lose a little capacity. Those particular battery strings lasted 4 ½ years, and if memory serves me correctly we changed 3 jars during the entire life of the string. So back to my original statement, I truly believe if we had measured battery temperatures in the recommended 77F – 82F range, we would have experienced a higher battery failure rate putting the customer more at risk.
One thing that I think should be discussed is an “equalize charge”. This seems to be becoming more and more popular, and I’ve noticed one manufacturer automatically does this on all new installs. Each battery manufacturer will recommend an equalize charge voltage. The equalizing charge will be several volts over float voltage. Float voltage is the charging voltage on the battery string. Float voltage is typically 2.26VDC per cell. So the typical UPS battery string has 240 cells at 2.26VDC/cell is 542VDC buss voltage. Equalize charge may be called out as something like 2.36VDC/cell to 2.41VDC/ cell. What that means is we are going to float the batteries at a much higher voltage than normal. The battery manufacturer likes to do this because it brings all of the batteries up above normal float voltage and allows them to settle into a nice even voltage on each jar. I believe this is becoming more popular due to the abundance of battery monitoring. The customer can see the new batteries immediately and see voltages all over the place. The typical equalize charge is 24 hours, and I have seen them as long as 72 hours. This is very hard on the life of the battery string because during the process you are boiling that string for the extended time. There are times that an equalizing charge may be required. It sometimes can “wake up” an older string of batteries (especially wet cells but that’s a whole different discussion), and it can help bring a string of batteries that have several batteries carrying low voltage up to a more acceptable range.
One last thing I want to touch base on, the author also commented that regular maintenance can help connections and clean corrosion. I agree totally about the maintenance helping maintain good connections if your service provider is doing a complete re-torque annually. As far as corrosion goes, if you are experiencing corrosion on a cable, there is a reason. Not applying an ample amount of No-ox during installation can cause the connection to get a small amount of corrosion but the main reason for corrosion is a post leak. The acid will wick up the post or leak around the post during a discharge. If the post seal is bad it will need to be replaced, because there is nothing that can be done to fix it. If you see excessive corrosion on a terminal, the battery should be replaced ASAP and the cable that has the corrosion should be replaced as well.
PS…. I bet you're glad you asked. Thanks for your time!