First make sure the new battery you got is good. After you are sure the battery is fully charged, either after cutting or using a charger, remove the negative cable from the battery and let it sit until the next cutting. If the battery remains fully charged, you have a parasite draw, which can be hell to find, even by an experienced technician. I had one which took weeks to find as it was also intermittent. Ended up being a frayed wire, about a 1/4”, that needed a little TLC to fix the problem. Patience will be your friend if you decide to tackle this type of electrical problem.