Older Mac G4 desktop. Wont power up. Already replaced battery

Hi,

There are basically two component types that change during storage; batteries and electrolytic capacitors. In addition, various surfaces (contacts, et cetera) may oxidise.

A logic board battery (typically, 3.6 V) may or may not affect the ability to start up.

Electrolytic capacitors have been known to cause major problems with older computers. An inspection using a magnifying glass may reveal leaking, discoloured or cracked components.

Which exact G4 Mac model do you have?

https://everymac.com/systems/apple/index-apple-specs-applespec.html#apple_mac_specs_g3_g4_g5

This

https://everymac.com/systems/apple/powermac_g4/specs/powermac_g4_400_agp.html

or this

https://everymac.com/systems/apple/powermac_g4/specs/powermac_g4_400_2.html

model?

The 3.6 V logic board battery should read at least 3.3 V. Generally speaking, inserting a battery the wrong way is not good (may explode). I do not know whether there is any reverse polarity protection.

In order to troubleshoot a computer like this one, you would really need more information. A web search for something like repair Power Mac G4 could perhaps be of some help.

Sorry, but information about the exact Mac model/year would help to begin with (see the individual specifications under the above link). Please do not post a serial number.

With most older Macs that used the 3.6V 1/2AA lithium battery, the polarity is printed on the logic board nextto the battery "cage" but may be very small. This is how it looks in my old (and dusty) G4 MDD 1.25ghz. I had to remove the dust to see the polarity markings (battery has been removed):