These two cartridges won't save after battery replacement
Pokémon Crystal and Silver versions. Replaced their batteries, both measure 3v, yet they cannot seem to keep the save working. What am I missing?
Update: they just needed another thorough cleanup with isopropyl alcohol and now work fine. Thanks for all the comments, I'll keep this post up for future reference.
The batteries measured 3V instead of 3.3V because I likely heated them up for a bit too long during soldering, but it shouldn't be an issue. Since I was getting comments from people saying it was the batteries' fault, I took a deeper look into this and found out that the SRAM chip only requires around 2.0V to store data (this is found under "data retention characteristics" in the datasheets of SRAM chips such as the ROHM BR62256F-70LL on the Silver cartridge [https://www.datasheetarchive.com/datasheet/BR62256F-70LL/ROHM?term=br62256&version=1](https://www.datasheetarchive.com/datasheet/BR62256F-70LL/ROHM?term=br62256&version=1) ).
The power protection chip on the MBC3 is an MM1026, which causes a maximum voltage drop of just 0.05V (found on its datasheet under VSAT1 [https://www.alldatasheet.com/datasheet-pdf/view/99104/MITSUBISHI/MM1026.html](https://www.alldatasheet.com/datasheet-pdf/view/99104/MITSUBISHI/MM1026.html) ), but as a rule of thumb in the community, you would consider a maximum drop of 0.3V "just in case". That would still bring the total power supplied to 2.7V (3V - 0.3V), which is well above the minimum voltage the SRAM needs. In fact, I have various older cartridges that save just fine at 2.7V. Of course, I wouldn't recommend relying on batteries that read less than 2.7V, as it gets too close to the safe threshold: 2.7 - 0.3 = 2.4V, which leaves little margin considering data corruption can occur around 2V (let's consider 2.2V just in case).
TLDR: While the heat stress slightly reduces overall capacity (shortening lifespan by maybe a year), any battery reading 2.8V or higher should provide plenty of voltage margin to keep your saves safe.