Lead acid battery tester

There are car battery testers that almost short-circuit the battery through a convoluted strip of metal which acts as a load resistor to simulate the current drawn by a starter motor. They incorporate a voltmeter so you can watch the terminal voltage fall on load.

It sounds as though the voltmeter in your case was calibrated with some arbitrary scale of 'goodness', based on 100% for a battery in perfect condition. The actual voltage drop will depend on many things, such as the battery capacity (which yours was compensated for) and the ambient temperature, so interpreting the readings calls for a degree of awareness and skill that most mechanics don't have.

However, it is usually a good enough indicator for obvious cases of dying batteries that collapse after a few tens of seconds or boil-up under heavy load.

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That's the case, the battery went down fast. The UPS software had the time to send me an alert email, but the event did not get written to disk logs. The battery would make 2 years in service next august.

I would have expected a much better lifetime than that, Does the charging system follow the battery manufacturer's guidelines? Continuous trickle charge can ruin a battery that isn't designed for it, some batteries thrive on an occasional discharge and re-charge.

Battery technology is extremely complex. There are so many ways of killing a battery; 'good practice' consists of juggling them to give the best compromise.

The brand leader American UPS company used to be noted for overcharging its sealed lead acid batteries (to be kind it could be called getting the maximum spec from the batteries) which probably shortened their life and there were published circuit board mods to stop it doing so.

That's a good question without an answer. It is a black box. I don't know what it does. Ok, it is a commercial UPS. I have found that some commercial UPS take care of their batteries better than others.

Another possibility is that the battery is lower quality, being no-name.

This UPS is a Salicru "UPS Soho+". The other one I have is an "Ellipse

Trickle charge in a traditional lead acid wet battery just "evaporates" the water in the electrolyte (ok, it produces some hydrogen). You just have to replenish the water periodically. But on these "new" gel types, the battery dies.

If that was a 12.5 volt battery (6 cell) his meter should not show 13.6 volts if it was correct . However the testers will put a heavy load on the battery and it should not drop but maybe 2 to 4 volts depending on the tester and the load it puts on the battery.. The less the better. If it drops more than that the battery is on its way to going bad. Simple volt meters tell almost nothing about a battery. They often have the rated voltage without a load. They must be put under a load. The more the voltage drops for the same type of battery the worse it is.