I’ve searched and searched everywhere and I just could not find any simple precise walkthrough WITH pictures. Hopefully, I will remedy this minor oversight and help out anyone who is willing to risk this simple procedure by writing my own instructions and archive with pictures, my attempt to replacing the battery to my Phantasy Star cart. This will be a step-by-step instruction on how to change the battery inside a Sega Master System game cartridge. The reason for me to do a Sega Master game is that there only a small handful of games on this system that require batteries and you don’t need a special security bit to open this cart; a common Phillips screwdriver is all you will need to do it.
I’ve placed an order for security bits and they should arrive later this week, but for all intents and purpose, this battery replacement walk-through should be universal and can be applied to Super Nintendo, Genesis, and N64 carts. I will be doing some more walkthroughs in the near future so that cautious gamers wanting a step-by-step guides for their specific game console will have it. 
It may seem a bit redundant but I know I would not have minded to have some redundant instruction on how to swap out batteries, anything to ease my fears of accidentally destroying a valuable game. This was my first attempt at a battery swap and I just wanted to show everyone how easy it can be. There are several walkthroughs online that require you to take an X-acto knife and break off the weld that connects the tabs to the battery. Being from the electronics field, I personally feel this method to be shoddy approach and can cause damage to yourself and game. Though I don’t agree with this method, you can follow the instructions at the Cheapassgamer forums or head over to Racketboy for such instructions.
My belief is that the only proper way of replacing a battery is to unsolder the old battery and resolder a new one. This is how the game was assembled from factory and I feel this is how the battery should be replaced. You will need to have some basic soldering skills to complete this task. This walk-through can be applied to any gaming cart that requires a small button 3V battery (with 2 pin leads), but because I can’t be sure of your soldering abilities and there is a potential risk since you are applying heat to a battery, I cannot be held responsible if you damage your game or hurt yourself. I repeat: I will not be held reliable for any bodily damage or damage that is done to your property.
Read here if you want to learn basic soldering. Soldering is a fun and simple hobby but if you are lacking the confidence to replace the battery, please seek out a local video games repair store near you and have a professional replace the battery.
One final note: you will lose your saves when you replace the save battery. There is no real easy way to avoid this problem. Yes there are complicated methods like adding a slave battery but I just find this method to be cumbersome and not worth the extra risk. With that out of the way, here is what you will need to replace a battery in a Sega Master System cart. Continue reading How to Change the Save Battery on a Sega Master System Cart
