First post, by Keatah
I recently fixed my old machine and got to thinking about why it would have 2 forms of battery backup.
It has (had) a 3.6v NiCd on the soldered to the motherboard, and the mobo will trickle-charge it. By calculations it should last 3 or so months with the power off. I thought it would be longer.
It also has provision for an external battery that is not charged by the mobo, there's a diode there. And it checks out. The system came equipped with 4.5v alkaline pack connected by wires and a connector. It can be replaced in a minute. Calculations show it's good for 4 or 5 years.
The batteries are wired such that the alkaline pack will charge the on-board NiCd cell.
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So why have two batteries going? Why not just go with the external pack and be done with it? What is the reasoning behind doing things this way?