I frequently have a need to prototype redundant power supply systems. For example, having two lithium ion battery packs powering a circuit with a plug-in charger. When the charger is plugged in, ideally, the batteries will isolate from the circuit and charge while the charger supplies power to the circuit.
Even better is to have three lines on the charger. One to power the circuit, one to charge battery pack number 1, and one to charge battery pack number 2. By isolating the battery packs from each other and from the main circuit charging can be done more rapidly and with greater safety.
The common technique for isolation is by diode ORing the batteries. However, this is pretty power hungry.
There exist some very nice devices used to create an ideal (30 mOhm) diode for this purpose (e.g., Linear Technologies, LTC4358 - http://cds.linear.com/docs/Datasheet/4358fa.pdf). These devices are invariably surface mount and would be far easier to use if you would create a breakout board for them.
Thanks for taking a look.
DrT