Small Engines (Lawn Mowers, etc.): 1989 craftsman, briggs and stratton, connector plug

Question
Back when I got the mower frame and deck etc.. I put a 12.5 briggs and stratton engine on it.. It started and ran good for a while..Then it started acting up and we jumped it off the selnoid for a while...then we replaced a fuse and it started with key again.. Now it will not start off te battery or selnoid so we have to jump start it everytime we need to use it..We thought the battery was shot so we put a new one in it and it started for about a week and then it ran that battery dead...and we had to start jump starting again...we also charged the battery but still no luck with key start or selnoid start..can you help me?

Answer
Can you send me the mower model number?  The format is xxx.xxxxx

Do you have a voltmenter?  Did the alternator/charging system of the new engine match the old engine?  Did the alternator/charging connector plug directly into the wiring harness?

Does the mower continue to blow fuses?
Let me know.
Eric