Installed 2nd battery but won't charge. Bad internal charger?

Crocdog, try to charge it with a Firewire charger. Check to make sure that your dock connector is clean, no debris, bend or corroded pins. You can also check the battery connector with the iPod plugged in to see if you receive any power from that. It should be around 4.2V-4.6V. Check the dock connector with a multimeter and see what voltages you get. The pinout for the dock connector can be found here. Yes, there are plenty of charging components on the logic board. All of them are SMC and would require a sound knowledge of soldering as well as the right tools. Hope this helps, good luck.