Conditions that are optimal for maximizing battery life cannot be met for each battery. Even if each cell in a battery could be made identical...and this is what battery manufacturers strive for when a battery leaves the production plant...each battery will, over time and during use, accept charge in different ways - they will age and deteriorate differently based on a number of factors.

So treating each battery in a string of batteries as if they were all average and capable of delivering a similar load is fine, but it's not right... because some of those batteries are going to be far from average- not to the naked eye or to the service tech who makes his annual pilgrimage to test them- but under daily, trended interrogation, each of those "black boxes" will reveal how capable they are of fulfilling their duty: To supply and sustain enough emergency power to transition from primary power to auxiliary power.

That is why monitoring batteries is so important, not just to identify that degradation is happening, but to detect precisely where in the string that degradation is taking place, so that you can create the conditions that are optimal for maximizing the life of your battery system.