Starting problem

You need to have the correct post design, mounting method, and physical size to match what the car uses. Very few people buy Ford batteries because they charge much more than necessary. Aftermarket batteries are fine.

You said you are having the same problem, but you did not say what that problem is.

You are describing a charging system problem. It is the job of the generator to recharge the battery after cranking the engine, and to run the entire electrical system. One way they can fail is when one of the six "diodes" fails. Those are one-way valves for electrical current flow. When one fails all you will be able to get is exactly one third of the generator's rated current. You did not list the engine size, so I guessed, and found a common generator for your car is a 120-amp unit. With a failed diode, all you will be able to get is 40 amps, but only at very high engine speeds, and that is not enough to meet the demands of the electrical system under all conditions. The battery will have to make up the difference until it slowly runs down over days or weeks.

The charging system needs to be tested by your mechanic, but you can start the test yourself with an inexpensive digital voltmeter. Measure the battery voltage with the engine off first. If it is good and fully-charged, it will be at 12.6 volts. If you find it is closer to 12.2 volts, it is good but fully-discharged.

Next, measure the battery voltage again with the engine running. It must be between 13.75 and 14.75 volts. If that is okay, it just means it is okay to do the rest of the tests, but that requires a professional load tester. Of particular interest is "charging voltage", full-load output current", and "ripple voltage". A few testers list an actual voltage for ripple voltage, but most just show it on a relative bar chart as "low" or "high". Post those values in your reply.