I have a G3 Lombard with similar issues. This thing refuses to see the battery, let alone charge it. I bought a new battery and external charger. The new battery took a charge, the old one flashed the charger light at me. This confirmed the old battery was toast. I also replaced the DC board and the charger board. The battery still refuses to show up. The battery has four lights on a full charge. I tried it in a friends Pismo and his Pismo saw the battery as expected. So the battery is ok and the problem is with my machine.

I read somewhere that one other possibility might be the mother board itself. If that's the case, I'll live with it tied to the wall since it also quit powering up my wireless card. I'm not going to replace the motherboard in a machine this old. It works great otherwise.