Interesting read, to condense it says each cell should give 2.061 volt and some voltage above that is required to ensure oxidisation does not damage the cell, both too much and too little voltage will damage the cell. So it would seem 2.17 volt is required per cell, which is all well and good for a single cell, but when the cells are used in series there is a likely hood that some cells will drop below the 2.17 volt while others will go above 2.17 volt.
So although 2.17 volt is correct for the cell, 13.02 may not be right for the battery.
If we look as charging systems over the years they have adapted. The old car had a free wheel on the dynamo and on switching on the ignition it would motor, once the engine was started it would then start to generate and the driver had to keep an eye on the ammeter and adjust the third brush to control the output required which would vary according to if lights were used or not.
The two bobbin regulator was a huge step forward the dynamo no longer started to motor when the ignition was switched on and the double wound coil one in series and one in parallel with the output automatically set the charge rate. For a 12 volt battery with battery disconnected from control box the open circuit voltage was set to 16 volt which today seems extremely high.
Even so the battery was used so much over time the cells would start to vary in voltage so we used a mains powered battery charger once a month to equalise the cells. Again the open circuit voltage seemed quite high, often one could measure 16 volts, depending on type of volt meter the point was there was no regulation it was simply rectified so even with a RMS of 14 volt the peak was 19 volt. As a result one could not leave the battery on charge for too long.
We started to get better chargers specially for traction batteries where there were two stages, it would charge until a set voltage was reached, then it would reduce output for a set time, this was called the equalising charge, however after that time it switched off. This again was improved with the three stage charger, first max current, then a high voltage typical 14.8 volt for 12 volt battery, and then the float charge of typically 13.2 volt.
At the same time cars got alternators and with some exceptions like the bus CAV203 alternator which did have current control, most did not have current control just voltage. The regulators used a reduced voltage this did vary between 13.4 and 13.8 with some special regulators which had a temperature sender under the ford tractor battery. This voltage seems to have creped up as vehicles use more electricity and 14.2 volt is not unknown.
The problem with the stage charger is the float is started when the current drops below a set figure. Often as low as 4 amp on a narrow boat battery, if something like the lights are used while it is charging then it will not drop into float charge. So the next generation is the pulse charge. With this a capacitor stores the energy which is then fed to the battery as a pulse, during the non pulse part of the cycle the voltage is measured and this controls the size of the pulse, this allows rapid charge while the battery is in use.
Some of the pulse chargers are add on systems, they take the alternator output and store it in a capacitor then turn it into AC transform it up and then use this higher voltage to pulse charge the battery, and it kids the alternators own regulator into thinking the battery is discharged.
Now the new generation is being controlled by the engine management so it switches off the alternator when engine under power and switches it back on when on over run, this is really causing a problem charging caravan batteries so now we use a DC to DC inverter to charge the caravan battery rather than the old type relays and blocking diodes.
So we can look at a float charge anywhere between 13.2 to 16 volt but in real terms 13.2 to 13.8 volt. What decides the float charge level is how often the battery is discharged. So for a car likely 13.8 volt or above. But for an intruder alarm 13.2 is ample. As the the UPS in question it would depend again on how often one gets a power failure but likely 13.2 is ample.
What would be good would be a charger which went to 13.8 volt after a power cut then after 12 hours dropped to 13.2 volt.
But this brings us around full circle to what I said to begin with, a battery lets say in a chair lift used every day with the voltage set to 13.8 volt per battery will likely last 4 years, but same chair lift used once in a blue moon likely only 2 years as the battery is being over charged, the reverse would also be true set at 13.2 used once in blue moon maybe will last 5 years, but used every day it will likely drop to 2 years.
The Ctec and the cheap Lidi look alike will likely work better than the original battery charger as it uses the pulse charge system. The solar panel chargers also use the pulse charge system and will take multi inputs i.e. wind charger and solar charger.
But the batteries cost £15 each, why worry? just change them every two to three years.
