It depends on what the UPS is doing and how it is made.
There are two main purposes in a UPS:
Ensure that the equipment plugged into it is kept live in the even of a power loss, over-voltage, or under-voltage condition;
Ensure that power line badness (spikes) are mitigated and the equipment protected.
Part 1 is easy to test, and most good UPSs will do a periodic test. This tests more than the battery; it tests the UPS itself and even to a lesser extent the equipment behind it.
Part 2 is harder. Many UPSs (and power strips) which claim to protect against spikes and lightening strikes do so using a small device called a metal oxide varistor. These devices sit on the input line and wait to catch a spike. When they do, they are damaged to some extent.
A nearby lightening strike can take them out completely, yet they will appear to be perfectly intact physically. Basically you can think of it as a can of paint you use to touch up a house. As you touch up more and more, your can gets empty, and eventually you run out of paint.
When these are damaged enough you start to lose fast-spike protection. In some areas it can take as little as a year to make a surge protector almost useless. In others, you may go for 10 without a problem if the input power is very clean.
So, to finally answer your question: I would consider replacing a 10 year old unit for this reason alone.
Another reason is that you can likely get a larger one for cheaper, it may be more energy efficient, and may even be smaller.
The OP questions is 5 years old, but the correct answer for the questions "Does a UPS lose its ability to protect equipment over time?" is yes, it does.
Surely UPS are designed to last longer than 10 years, but
they require proper maintenance and environmental conditions
even so, some components degrades over time
Because unlike other IT equipment UPS deals with high currents and power, there are 3 main components in any UPS design: charger, rectifier and inverter. Most recent technology uses IGBT gates, but even those wears down and have a limited life time by nature.
Some links regarding life time of IGBT inverters for solar panels, chips/IGBT modules are essentially same, they are widely used in devices like welders, hybrid cars, wind and PV power generators.
On larger UPS systems, simple on time replacement of dust filters is important procedure, failing to do so could affect cooling the essential components like inverters and they life span would decrease substantially. For example MGE UPS requires periodic service and maintenance by certified Field Service Engineers, they have a special tools and software for diagnosing many UPS components including battery charger, AC capacitors etc. High capacity electrolytic capacitors are also used in every UPS and in higher-than-normal temperatures their electrolyte vaporises and leads to failure. Such preventive maintenance allows to detect degrading components earlier and replacing them before thier ultimate failure.
If it's treated well then the only thing that should really wear out is the batteries, so as long as these are maintained and test regularly you should be fine.
That said, you may find that your older UPS's are not as economical or 'green' and you may be able to reduce power consumption with a new UPS (if that is something you are concerned about). However, whether the outlay on a new UPS would be recouped by the energy savings is hard to say.
Ignoring the batteries, a UPS is just another piece of electronic equipment. Unless components fail or are degrade beyond tolerances the UPS will continue to function indefinitely. As components can and do degrade over time, although vastly less than they did "in the old days", the UPS may benefit from a recalibration, so that the various trigger points are accurate.
Calibration, together with an overall check of the device, is normally a procedure best left to specialists. As this should be a relatively small price (about $120 Australian a couple of years ago for a UPS worth $3,500) it is worth getting done. The calibration procedure should also detect if components are far enough out of spec to be a problem.
It depends on what the UPS is doing and how it is made.
There are two main purposes in a UPS:
Part 1 is easy to test, and most good UPSs will do a periodic test. This tests more than the battery; it tests the UPS itself and even to a lesser extent the equipment behind it.
Part 2 is harder. Many UPSs (and power strips) which claim to protect against spikes and lightening strikes do so using a small device called a metal oxide varistor. These devices sit on the input line and wait to catch a spike. When they do, they are damaged to some extent.
A nearby lightening strike can take them out completely, yet they will appear to be perfectly intact physically. Basically you can think of it as a can of paint you use to touch up a house. As you touch up more and more, your can gets empty, and eventually you run out of paint.
When these are damaged enough you start to lose fast-spike protection. In some areas it can take as little as a year to make a surge protector almost useless. In others, you may go for 10 without a problem if the input power is very clean.
So, to finally answer your question: I would consider replacing a 10 year old unit for this reason alone.
Another reason is that you can likely get a larger one for cheaper, it may be more energy efficient, and may even be smaller.
The OP questions is 5 years old, but the correct answer for the questions "Does a UPS lose its ability to protect equipment over time?" is yes, it does.
Surely UPS are designed to last longer than 10 years, but
they require proper maintenance and environmental conditions
even so, some components degrades over time
Because unlike other IT equipment UPS deals with high currents and power, there are 3 main components in any UPS design: charger, rectifier and inverter. Most recent technology uses IGBT gates, but even those wears down and have a limited life time by nature.
Some links regarding life time of IGBT inverters for solar panels, chips/IGBT modules are essentially same, they are widely used in devices like welders, hybrid cars, wind and PV power generators.
On larger UPS systems, simple on time replacement of dust filters is important procedure, failing to do so could affect cooling the essential components like inverters and they life span would decrease substantially. For example MGE UPS requires periodic service and maintenance by certified Field Service Engineers, they have a special tools and software for diagnosing many UPS components including battery charger, AC capacitors etc. High capacity electrolytic capacitors are also used in every UPS and in higher-than-normal temperatures their electrolyte vaporises and leads to failure. Such preventive maintenance allows to detect degrading components earlier and replacing them before thier ultimate failure.
If it's treated well then the only thing that should really wear out is the batteries, so as long as these are maintained and test regularly you should be fine.
That said, you may find that your older UPS's are not as economical or 'green' and you may be able to reduce power consumption with a new UPS (if that is something you are concerned about). However, whether the outlay on a new UPS would be recouped by the energy savings is hard to say.
Ignoring the batteries, a UPS is just another piece of electronic equipment. Unless components fail or are degrade beyond tolerances the UPS will continue to function indefinitely. As components can and do degrade over time, although vastly less than they did "in the old days", the UPS may benefit from a recalibration, so that the various trigger points are accurate.
Calibration, together with an overall check of the device, is normally a procedure best left to specialists. As this should be a relatively small price (about $120 Australian a couple of years ago for a UPS worth $3,500) it is worth getting done. The calibration procedure should also detect if components are far enough out of spec to be a problem.
If the equipment is operated under ideal conditions they should last for a long time.
It might be a good idea to setup some kind of testing schedule to verify they are still working.