> The CMOS bat on an old compaq machine has died. It's 3.6v Yeah batteries do that. ;)
Four bucks fifty for a lithium round flat one at the local supermarket. Numbers are CR2016 to CR2032, the thicker, the more capacity. Buy the thickest that'll fit the holder on your mobo. > I'm replacing it with AA bats... 2 won't be enough --> 3v It depends on the chip. You should be able to locate the chip in question - google for its specs and find its battery backup voltage range. Chances are good that 3V are sufficient, I haven't seen any mobo with something other than a flat-disk battery in a long time. Easy to find out with 2 alkalines... Leave the thing off overnight and check the CMOS settings in the morning. > 3 * 1.5v = 4.5v. Will that upset the mbd? No, those electronics are fine up to 5V +-5% (with the exception of CPU core and memory voltages, which are lower). However, you're bringing up the supply from data retention to close to operating voltage, which might cause a significantly higher drain on the batteries. > If I use 3 AA bats in series it will give me 4.5v. Does anyone know if > this will cause an issue? It won't cause any damage. It'll probably work as you expect. While 3 rechargable batteries will give you in the order of 3.6V, the lack of an in-circuit charging facility for these together with their cost being several times that of a lithium cell which lasts until the mobo turns to ashes makes it a bad idea unless you really need it, but hey, it'll work. Well until they've run flat or have self-discharged. Say about a year for NiMH. Btw the battery supplies the CMOS only while the computer is turned off, so if you're talking about some always-on router here, the battery you stick in now will outlive the silicon. Volker -- Volker Kuhlmann is list0570 with the domain in header http://volker.dnsalias.net/ Please do not CC list postings to me.
