Alternator prob. Diagnose Ford zx2 98 Why won't the battery hold a charge?

My '98 escort zx2 has started acting up(again). About a month back there was a three day stent where the car remained parked. It started fine and ran like normal, and got me to destination a. Left in accessory mode for about 10 minutes waiting on food seemed to drain the battery as it no longer had the power enough to turn over. Still power to all functions. A jump got me home, and for the next few weeks all was fine. Now I'm having the same issue. It either starts up fine, or doesn't successfully turn over. I replaced the battery and put in on a charge overnight, and that too bought me a few days. The most recent jump took almost five minutes connected to the donor car before it would start. Second thought is alt. Went bad. But it confuses me that once running the car seems fine. Hence the reason I'm here seeking your advice. And thanks in advance for your time and effort.

Check all connections for clean and dry plus tight.
As battery has been replaced it's likely our alternator is failing or we have a power drain.
Look up how to check for power drain on u tube. Alternator testing is also possible though many prefer a garage do so. From symptoms it's either an alternator diode failure or parasitic battery drain eg circuit drawing power we not aware off.

Tighten your battery cables including where the ground connects to the frame and block, then put a volt meter on it to see if it's charging.

If not, replace the alternator.

#1. Remove the battery and take it to any store that sells new ones other than Auto Zone. Ask for a free 15 second *load test to see what the reserve amperage capacity is. Amperage spins starter motors nor voltage.

#2. When a new battery has been installed start the motor and touch the battery terminals with an inexpensive volt meter set @ 20 volts. IF the alternator is charging properly the volt meter will read between 13.5 - 14.2 volts.

Leaving the jump leads connected and the other car running for 5 - 10 minutes puts power back into your battery and should be done every time as it makes it easier to start your car. The fact that it starts with jump leads means there's no problem with Starter system. So it is either Charging system, Battery or bad connection.
Whilst you have the jump leads on and the other car running get a Volt Meter and Read across your Battery and slowly rev the other car, It should go up to 14.5 Volts and no more. This shows you a good charging system. When you start your car remove jump leads and do the same again.
If it goes up to 14.5 Max Volts your charging system is OK
If it goes over 14.5 Volts the Voltage Regulator needs replacing (Part of the Alternator) and may have cooked the battery.
If it does not get up to 14.5 Volts Your Alternator may need replacing. Or it may just need the Drive Belt adjusting (Normally this is indicated by the Red ignition light staying on)
After you switch off your car take another reading, It should be 12 Volts, If not the battery is no good or a bad connection has stopped it getting charged.
If it does leave for 20 minutes then Re-Check, If it still says 12 Volts your battery is OK if not you may have a dead cell. Batteries are 6 X 2 Volt cells but only give you 6 X lowest cell so 6 X 1.5 Volts = 9 Volts.

Andy C