This MS-7LA calculator came in for recycling last year. It did not power on.
It is the holidays at present so I thought I would do some holiday hobby work (repairing things is one of my hobbies).
I undid the three screws on the back of the calculator and the back cover come off fairly easily. The leaky battery was easy to spot. I cleaned the circuit board and put in a new battery. Still no go! On closer inspection the circuit board pad looked a bit tarnished. I then spotted the completely corroded PCB track that would have been where the interface between the anode and cathode of the leaky battery was positioned.
I removed the battery clip, cleaned the anode terminal, and added a wire link (the blue wire in the photo below) to fix the corroded track.
With the battery back in the calculator was back in operation.
That all took me about 20 minutes. At our current labour rates that would have cost a customer $26 for the labour alone and at our current minimum repair fee cost it would have been $35. The battery costs $3.25 or $5.00 for one of good quality.
You can buy a roughly equivalent calculator of a well known brand for less than $4.00. The current Casio equivalent sells for $20 but I can probably only get $5 for the one that I repaired.