If you look at the schematic of TAF (which you reference) the Vbatt from the batteries goes to the RAM chip, ASIC and a bunch of other stuff which some controls and keeps track of time. Obviously when you remove the batteries that voltage goes away. The NVRAM can't push any voltage out to keep those running when the game is off. You'd have to go back to batteries to do that.

Now I'm not familiar with the pin-outs for the NVRAM but the Vbatt pins may not be connected to anything internally so running batteries and a NVRAM may be fine. But there are some jumpers on the Vbatt line that can be removed to isolate the RAM chip from battery voltage.

You'd basically have to find a NVRAM chip with voltage output to drive all the other stuff. I don't think that exists. And if it did you'd have to recharge the batteries and now you're into leakage issues again. You could make a plug-in power supply and connect to the Vbatt terminals, but if the power goes out or you unplug the game you'll lose the time. I'd suggest understanding the schematic and NVRAM before you start running 2 sources.

I run Energizer Lithium AA batteries in all my games. I just did this to all of them a few years ago (2016 perhaps). I have spot checked some by pulling them out with the game on and testing voltage. The ones I've pulled were well over 1.6V each. I did have one game with something bad on the board that was killing even the Lithium Energizers. I thought it was the blocking diodes and I replaced those and still the same issue. I did end up putting NVRAM in that one game and all is fine now, but obviously no clock.

Nope. Just replaced alkaline with lithium.

Nope. Original WPC95. It was weird that only one of the cells went dead, the other two were fine. Defies logic if you ask me.

No. With 32 other games all running Lithiums and just this one taking out a single cell, whether lithium or alkaline, I didn't think that would matter. All batteries were bought at the same time from the same vendor in the same bulk pack. I've not had a single issue with any other cell in any other game.

Hmmm. I'll have to check and see. Although it's not either game it could be the issue. Thanks for the link.

Prototype machine serial 00001. So I have no idea if it was grabbed from another machine when they were building it or what. There are no serial numbers on the boards, just the cabinet. Anyways, NVRAM installed and problem is gone... so far.