Batteries & save batteries

Save batteries keep the high scores and saved games inside retro cartridges. This page brings together 3 V CR1616, CR1620 and CR1632 lithium coin cells, the 28-pin FRAM memory chip FM1808, FM18W08 or FM16W08 that removes the need for a battery, and the RetroScaler real-time clock board intended for the MiSTer FPGA.

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Batteries USB-C 8 Modules de charge 9 Condensateurs & recap 3 Piles & sauvegarde 3

Coin cell, FRAM chip or real-time clock: three answers to the same symptom

Identify the exact format before desoldering

The four digits of a coin cell give its dimensions. A CR1616 measures 16 mm across and 1.6 mm thick, a CR1620 goes up to 2.0 mm and a CR1632 to 3.2 mm. All of them deliver 3 V, but the energy reserve grows with the thickness. A holder designed for a CR1616 will not take a CR1632: read the reference printed on the original cell rather than judging it by eye.

FRAM does more than replace the battery

The 28-pin FRAM chips FM1808, FM18W08 and FM16W08 keep the data without any power at all. They take the place of the volatile memory in a cartridge or a board, which removes the battery for good along with the corrosion it eventually causes. In exchange, you have to desolder a 28-pin package and check the pinout: these three references are not always interchangeable depending on the board.

What it doesn't do

Replacing a battery does not restore a save that has already been erased. The RetroScaler RTC board handles the clock of the DE10-Nano in a MiSTer FPGA, not game saves. And none of these solutions recovers the contents of a memory chip that is physically dead.

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Questions fréquentes

How can I tell whether my cartridge battery is dead?
The clearest sign is losing the save every time the console is switched off, or an internal clock that goes back to zero. A multimeter settles it: a lithium cell rated at 3 V that has dropped well below 2.5 V no longer holds the memory.
Does the coin cell have to be soldered?
On an original cartridge the cell is held in place by soldered tabs, not clipped in. You can solder in a new cell with tabs, or fit a holder so that later replacements are immediate. In both cases you have to work quickly so as not to heat the body of the cell.
Does the FRAM chip suit every cartridge?
No. It replaces a 28-pin memory with a compatible pinout, a common situation but not a universal one. Check the reference printed on the original chip before choosing between FM1808, FM18W08 and FM16W08, and plan on desoldering a 28-pin package.