It's good to see this getting some attention. People should know that removing batteries and replacing them with something modern, particularly non-leaking modern, is a good thing.
Most motherboards work with 3 to 4.5 volts. If a circuit doesn't charge, then it's a simple matter of using two or three AA or AAA batteries. If it does, we can use rechargeable batteries (I've a box of Ikea ones), or we can put a diode in line.
For instance, here's a replacement set for a Quadra 630 motherboard: