In Need of desperate help.

I have a 2004 Subaru Forester XS, 250k original miles. I've been having some issues with it the last few weeks.
Occasionally I would go to start the car and all of a sudden it would crank just fine then I'd crank it half way and boom the battery would die almost instantly, that has happend a few times even with a good battery.
The one night I pulled up to Applebee's and shut the car off and for the hell of it I tried to crank it to see if it would start up again and sure enough the battery instantly died again, had to call for a jump start let it run for 15 min then shut it off. when I came out of a restaurant to start it again I noticed the gas tank was pretty low and i got it started with a jump pack. About after 2 min of letting it idle I started driving and it started sputtering as if it was out of gas , it sputtered all the way to the gas station and it wouldn't accelerate even with the pedal fully matted to the floor no acceleration just a constant speed of about 15 miles an hour and loud popping sounds from the air cleaner box. Engine would shake like hell and pop loud Even when I'd down shift there would be no acceleration. I just changed oil a couple hundred miles ago and ran beautifully before I got to Applebee's , Made it to the gas station put about 5 gallons in and problem went away for about 2 min then it all together died again.
Today I changed the alternator with a used one with far less mileage on it checked to see if it was working before and it was, was an another forester before that I listened to and examined before taking the alternator out, same exact alternators and swapped it out and was running great drove it for about 30 minutes no popping , no shaking , smooth like usual , and then all of a sudden power steering went out, dash lights went off, headlights etc. but ABS,Break, Air bag lights all came on. Sputtering came back and loud popping with no acceleration. Alternator is shot once again. I'm not sure what to do at this point. Either sell or scrub because I've never had this type of issue with a car. Unless somebody else has had this experience and knows a solution or if anybody can help. Thank you for any help , I've put 15k miles on this in the last 4 months after I bought it from the original owner who doesn't rember the last time maintenance was done , all I've done was oil changes but haven't touched sparks or anything else. 250k miles 5 speed manual , clean title
Thank you for any help, I'm carless as of now and dont really want to give up this car.

 

Have it towed to a reputable shop, or have someone you trust take a look at it. Symptoms kind of sound all over the place. This may sound stupid, but have you checked your oil levels? Maybe you have an oil leak. Not uncommon with a subaru. I am not an expert by any means. Good Luck dude.

 

You say even with a good battery. Have you had the battery checked under load? Alternator output? How do the wires/plugs look?

 

I would not drive it and instead get it towed to a good shop and have them diagnose. Have them do a thorough check out, I hope the timing belt has been changed at some point...

 

I had the symptoms described except the alternator issues and it was solved with a new 255lph walbro fuel pump. Not sure where the alternator issue would be involved in there unless there is a short in the internal wiring for the pump. No pro by anymeans but have ran into this on a truck a buddy had back in the day. Hope this helps

 

I pm'd you a little while back about coming and looking at it but I havent gotten a response but I understand ppl are busy but the offer still stands if you want another set of eyes looking at it