Why Does my save randomly delete after a fresh battery change?

I've been Resoldering new batteries into my old Game Boy Cartridges to keep the save feature in working order. After the battery replacement the saving seems to work but then will end up deleting at random. I made sure to do the following

• Correct polarity alignment for the battery
• Desoldering the pads and adding fresh Solder of the same chemistry
• Checking continuity and avoiding cold solder joints
• Reflowing all chips and pins on the PCB
• Cleaning the board with IPA

I've tried everything within my soldering capabilities and yet multiple freshly changed cartridges continue to lose save data at random intervals. Any help or insight would be greatly appreciated. I'd like to get back to playing with peace of mind.