Memory-battler,
I'm glad that you found my battery replacement guide useful. In response to your question, yes I think the same method of battery replacement could be used for Ruby or Sapphire.
Even though a GBA cartridge is smaller than a GBC cartridge, if it uses a battery, it will be connected the same way. I found pictures of some GBA carts, and they look like the battery is connected the same way, using tabs that are soldered to the board.
http://babelfish.altavista.com/babel...katorittu.html
If your RSE battery dies, you can replace it with another 3 volt battery. You mentioned the CR1616T. That has a 55 mAh rating, which is much lower than the 165 and 220 of the CR2025 and CR2032 that you can use in a RBY or GSC cart. While it may last one third the time as a CR2025 under the same load, there is a chance that the GBA chips may draw less power and therefore don't need as large a battery.
Just find a 3 Volt battery that is thin enough to fit in the cart, and it should work fine. (The CR1620 is only 0.4 mm thicker, and has a 75 mAh rating, so that may also work.) You will just have to be very careful when soldering because the GBA cart looks like it may have its components more closely packed than in the GBC carts.
One warning in battery replacement. If you still have an active game save, you will need to make sure that you trade your characters to another game before replacing the battery because once you remove it, all game save data will be lost. The only way I can think of to replace your battery without loosing your data is to solder leads from a 3v power supply onto the cart before starting. Then when you remove the battery, as long as the flow of power is not interrupted, the data should remain while you connect the new battery.
I hope that is a help for any of you who were wondering about the GBA games. If anyone has any other questions, I will do my best to answer them.
On a semi-related note, have any of you ever heard of the battery dieing in any games other than Pokemon GSC? That is the only time I have noticed that happening. All my other games for the original Game Boy still work fine. I guess it may just be a result of the clock and the frequent saving that is done in GSC?