The fact that it was a 3-month-old new UPS is a major part of the problem see
Bathtub curve - Wikipedia
meaning any brand new device is of suspect reliability until any
manufacturing defects (not enough thermal grease / incorrectly applied thermal grease - poor solder joint or stray piece of loose solder creates a short circuit) or
component defects (the PCB components the manufacturer buys in to populate the Printed Circuit Board - the batteries are also bought in from a 3rd party and assembled into a battery pack for the UPS) have had a chance to make their presence felt.
Once something is around 2 years old the chances are nothing will then go wrong for a long time - as long as you replace the UPS batteries when the monitoring system tells you to AND use good quality batteries.
It is surprising what low cost garbage brands of batteries come in most UPS manufacturers pricey battery packs - that is why they tend to use double sided tape to glue the batteries together (the supplier name is under the double sided tape on packs made up of 2 or more batteries) so you cannot normally see who is supplying batteries to the UPS manufacturer - often an unknown Chinese battery brand and if they have a website it is always the battery model the battery maker openly admits is the least durable, has the shortest service design life [stated in years] and has the lowest energy density of the entire model range.
Of course the worse batteries that come with the UPS the shorter they will last, the faster you will buy a new battery pack OR if the batteries take out the UPS - you will just end up having to buy another UPS - it is a very cynical but effective business model for selling UPS's!
You can get thermal interface pads to use instead of thermal grease - which should in theory never dry out - but you would have to investigate the ability to conduct heat of the pad versus the grease otherwise you might cause overheating (there are datasheets for all thermal interface methods that give the heat conduction values so comparisons can be made for the product design stage) - having said that I have plenty of devices around me - some are vintage electronics - and the original thermal grease is still (apparently) working just fine - again question of quality of the brand of grease as well as circuit design - if a power component is not given enough thermal headroom and big enough heatsink to be effective the device will fail early - which of course sells another device
Used to drive past several franchised luxury car dealerships each morning and regularly get stuck in traffic when the double deck car transporters appeared each week half blocking the roads to deliver the brand new cars to the dealerships.
What was interesting was some new cars would be absolutely stuck fast on the car transporter and could not be unloaded - more interesting still was when it was the last car to go on the transporter so it blocked absolutely everything else onto the transporter.
The problem was the drivetrain (gearbox or differential) had seized up so it was impossible for the driven wheels to turn - they had to be unceremoniously dragged off by a tow truck or by a winch depending on which way round they were pointing on the transporter.
I wonder if they were rejected by the dealership as faulty goods and then what happened to those cars?
Sent back to the factory/importer - doubt they were scrapped - they were probably fixed by the bought in sub-assemblies of gearbox or differential being swapped (most car makers do not make their own gearboxes / differentials / steering gear - it is all bought in as readymade sub-assemblies) - so were those lemon vehicles then sold as new?
Often the NOT brand new car or device is MORE reliable and safer than the untested / unknown brand new item.
It is all quite the conundrum!
