GTA02 RTC backup battery
RTC keeps the current time while Neo FreeRunner is off or suspended. Rechargable lithium backup battery should keep clocks running for hours when main battery is flat or removed, but it has limited lifetime.
Replace by capacitor
RTC backup battery (BAT1701: HB414-IVO1E) can be replaced by electrochemical double layer capacitor (EDLC), like XH414H-II06E (apparently obsolete, not recommended for new design) or EECEN0F204 (500 Hrs @ 60°C) (datasheet). These supercapacitors have much longer lifetime and they are less sensitive to heat from solder iron than lithium baterries.
Alternatives - untested:
(search digikey.com) ? What terminal type?:
- DSK-3R3H224 (1000 Hrs @ 60°C) Only 4.8mmDiameter
- KS-3R3224 (1000 Hrs @ 70°C) Obsolete.
- EDLEN204 (1000 Hrs @ 60°C), Datasheet quote: "...Temperature Factor. To determine the effect of temperature on expected life of a supercapacitor, use the fact that expected lifetime doubles for each 10 °C that the operating temperature is reduced. As an illustration, at 85 °C and full voltage the rated lifetime is 1000 hours. So, at 40 °C the expected lifetime would be multiplied by 2^((85-40)/10) = 2^4.5 = 22.6 times. The Temperature Factor is 22.6, and for 1000-h, 85 °C rated life, the expected 40 °C life would be 22600 hours..."