replacing the original batteries with a lithium battery is the way to go except for games like twilight zone and any other game that uses the clock on WPC / WPC 95 machines.
even though the clock doesn't reset to default on WPC and WPC95 with a 3 volt lithium battery they do lose time.

Please excuse my ignorance, what exactly do you mean?  I assume lithium AA batteries would give no problems or is this a mod where you can fit another lithium solution.

I've been using remote packs on mine and lithium AA on high end ones that I don't won't to tamper with.