My brake light is blinking on my 91 Honda accord and i'm having trouble starting it?

I recently had a rebuilt engine put into my 91 honda accord. I've been driving it for about two weeks and about three days ago the battery died so i got a new one with the warranty i had. But that only worked for a couple days now when i go to turn it i have to turn the key and hold it for about ten to twenty seconds for it to start. It slowly turns and turns till the belt catches i need help please

Your battery is loosing charge. Have someone check the alternative and check any shorts in the car

Test the alternator output - leave the engine idling, turn on the high beams and blower motor on high. Attach a multi meter from the alternator output terminal to ground and watch the voltage. Should remain above 13.8v after 10 minutes. If not, replace the alternator, belt and external regulator if applicable.