Early warnings you can check yourself between services
Your ears and eyes do the rest. A crank that sounds slower on the first start than it did last month is capacity leaving the building. Open the bonnet quarterly and look at three things: white or green crust on the terminals, which strangles current flow; case sides that bulge outward, which is heat damage and a replacement trigger on its own; and dampness or a sharp sulphur smell around the battery, which means it is gassing or leaking. On most UAE-market batteries there is also a date code stamped into the case or printed on a label, so you can establish the true age of the battery in a car you bought second-hand rather than trusting the seller's memory.
None of this replaces a proper conductance test, but it changes the timing of everything. Owners who spot the 12.2V trend in March replace on their own schedule, at a normal price, from a shortlist of vendors. Owners who wait for the no-start discover it in an August basement and take whoever can come fastest. The whole economics of battery replacement in this country favours the person who moves three weeks early.