Your UPS has a battery inside it. Usually it is a lead-acid type (those are the least expensive for the manufacturer), but both lithium and gel-cel batteries are sometimes used.
The battery is by far the most vulnerable and failure-prone part of your UPS. If you have your UPS long enough, you will probably have battery problems. Once every six months to a year or so you should recalibrate your UPS's battery sensor, and once every several years you will have to replace the batteries.
To extend your battery life, (a) avoid deep discharges, and (b) don't expose them to extremes of heat, cold, or humidity. Unfortunately there is not much you can do to avoid deep-discharging your UPS other than living in an area where power outages are few and short.
Your UPS's dwell-time calibration will lose accuracy over the life of the battery. The usual symptom of this problem is that the UPS overestimates the dwell time it has remaining during outages, but occasionally it can also lead to an actual bad-battery condition going undetected and very odd symptoms as a result.
UPSes have a recalibration procedure built into their firmware. It generally involves deep-discharching and recharging the battery while the UPS is in a special test mode. Your recipe for triggering such a recalibration will vary according to your UPS software.
You always need to do this when you install new batteries (see below). It is a good idea to do it once every six to twelve months as routine maintenance, but no more often than that; as we noted previously, deep discharges shorten your battery life.
All modern UPSes have a low-battery alarm and run a periodic self-test; they will alert you when replacement is needed. Usually they both flash an indicator and make an alarm sound. If you have a monitoring daemon set up, they will alert it and you will probably get warning mail. If you ignore the alarm it will time out, but be repeated at intervals.
You will occasionally get a false alarm. It's a good idea, if you get an alarm, to explicitly trigger a UPS self-test the next day and see if the alarm goes away (the procedure for doing this varies depending on your UPS software). If the alarm is persistent, you need to replace the batteries.
It has been reported that bad batteries can also produce symptoms that mimic inverter failures or wonky control electronics. Even if your UPS is displaying epileptic symptoms like repeating alarms and flashing panel lights, a bad battery is the first thing to suspect.
UPS manufacturers would of course prefer that you replace your entire UPS when the batteries die, since they make more money that way. But in fact there is nothing unique or magic about UPS batteries. They are standard types also used for other applications such as powering marine electronics, with standard connectors. You can buy them from sources other than the UPS manufacturer, and sometimes replace them with equivalents that are better and less expensive.
It's best to wait until the low battery alarm before ordering a replacement; keeping batteries on the shelf reduces their life unless you keep them fully charged.
Do not throw old batteries in your regular trash! They contain toxic metals and acids. Be kind to your environment and hand them to a qualified party for recycling. Most battery dealers will cheerfully do this for you. If not, your local garbage company or waste-disposal authority can explain to you how and where to turn them in safely.
Below, you will find some suggestions for buying replacement batteries. One important note of caution: at least one user purchased one of the aftermarket batteries noted below and found out that they would not fit into his unit. This required cutting and soldering and other very undesirable things, so be extremely careful in measuring your batteries — including every millimeter of the terminal connections, which can cause problems.
Although you can do a hot swap of your batteries while the computer is running, it may not be very satisfactory, because the unit will not know that the batteries have been swapped and your monitor daemon will continue to show a low-battery indication. To correct this situation, you must do a discharge and recharge of the battery. At that point the battery should be calibrated better.
It may take several discharges and recharges of new batteries before they reach full capacity and the dwell-time calibration is accurate. If your UPS contains two or more battery units and your monitoring software reports separate voltage levels for them, one way to tell is to watch the divergence in voltage levels. As the cells reach nominal full capacity, their voltages should converge.
APC makes "Replacement Battery Units" for each of the SmartUPS models, but they sell them directly only in the U.S. Your local Yamaha SeaDoo shop (if you have one) carries 35 ampere-hour deep cycle marine batteries that are direct replacements for the kind APC uses in many of its models. These are gel-cel and will double the runtime and/or cut your recharge time in half. Here are some West Coast sources:
Jet Works 1587 Monrovia Ave. Newport Beach CA 9266? Tel: +1 714 548-5259 J-W Batteries, Inc. Tel: +1 714 548-4017 WPS 49-1200 GEL-CELL KB-35 BATTERY
The company I've heard most strongly recommended (by Carl Erhorn, a core developer on the apcupsd project) is called Battery Wholesale Distributors of Georgetown, Texas. If you have questions, you can reach them by phone at (800) 365-8444, 9:00AM to 5:00PM (their local time), Monday through Friday. Carl reports having gotten email from them on the weekends, although the office is not open then.
The web site, with current pricing, is www.batterywholesale.com. They will ship outside of the US, they take all the usual credit cards, and they accept orders by phone or Web.
Carl reports that BWD has found manufacturers who make batteries in the standard case sizes, but have additional capacity over original UPS batteries. Often, the difference is as much as 15% or so, and this can result in additional runtime. It's a nice upgrade for a minor increase in price.
BWD is also 'green-aware', in that they encourage you to recycle your old batteries, and will accept the old batteries back from you if you cannot find a local place that recycles them. You pay the shipping but other than that, there is no charge.
Carl says "I've been very pleased with their products, service, and pricing. I hope you find them as helpful to you as I do. I've been dealing with them since about 1994, and have never been disappointed. The owner of the place also is very good on technical issues, so if you have questions on their products, he can get as technical as you need to go."