I've removed the lithium PRAM battery from my SE/30 and replaced it with a 3-cell, 3.6V, 80mAh rechargeable NiMH battery and a simple charging circuit:
The NiMH battery is about the same diameter as the original, but shorter. If you want to keep the socket, the tabs on the battery could be bent outward to make contact, but I chose to solder directly to the logic board.
With even occasional use of the machine, the battery should stay charged and eliminate the explosion/leakage risk of lithium cells.
Two components are added between pin 8 of the RTC and the battery to allow charging: a 1N4007 diode and a 56 Ohm resistor:
5V is dropped to ~4.4V through D2, then to ~3.8V through the new diode. If you want to tap a 5V source directly, you'll need an extra diode.
Battery voltage with power off: 3.740V
Battery voltage with power on: 3.747V
The SE/30's standby circuit pulls 5.8uA. With 80mAh of capacity, the battery should last for 19 months, ignoring self-discharge.
On the Color Classic, @JDW measured 63uA, which would drain the battery in only 1.7 months.
I have used Eneloops in a vintage PC with good results. That may be a better way to go with higher drain standby circuits.
Since I've just done this mod, I don't have any long term results. My machine is used fairly often. Otherwise, I wouldn't have soldered the battery.
Amazon.com: New Ni-MH 80mAh 3.6V Rechargable Battery Cells with Tab : Cell Phones & Accessories
Amazon.com: New Ni-MH 80mAh 3.6V Rechargable Battery Cells with Tab : Cell Phones & Accessories
www.amazon.com
The NiMH battery is about the same diameter as the original, but shorter. If you want to keep the socket, the tabs on the battery could be bent outward to make contact, but I chose to solder directly to the logic board.
With even occasional use of the machine, the battery should stay charged and eliminate the explosion/leakage risk of lithium cells.
Two components are added between pin 8 of the RTC and the battery to allow charging: a 1N4007 diode and a 56 Ohm resistor:
5V is dropped to ~4.4V through D2, then to ~3.8V through the new diode. If you want to tap a 5V source directly, you'll need an extra diode.
Battery voltage with power off: 3.740V
Battery voltage with power on: 3.747V
The SE/30's standby circuit pulls 5.8uA. With 80mAh of capacity, the battery should last for 19 months, ignoring self-discharge.
On the Color Classic, @JDW measured 63uA, which would drain the battery in only 1.7 months.
I have used Eneloops in a vintage PC with good results. That may be a better way to go with higher drain standby circuits.
Since I've just done this mod, I don't have any long term results. My machine is used fairly often. Otherwise, I wouldn't have soldered the battery.
