Home theater power conditioner is probably something you have to worry about only if you have a very serious system in place. Also known as AC regenerators, these devices take AC wall power converts it to DC power, and then reconverts it back to "clean" AC power. The idea behind this is to protect your equipment and possibly improve the quality of image/sound. A backup battery is something that you should think about if you live in an area with frequent blackouts and generally unstable electric power. Not a bad thing to have if you want to make sure that your devices do not have to be reinitialized every time there is a power outage. Both these features (power conditioning and battery backup), along with voltage regulation are combined (rather inexpensively!) in APC AV H15 Home Theater 1500VA Power Filter and Power Conditioner:
From APC's power engineering labs comes the H Type Power Conditioner, a single unit that delivers pure, stable power for high performance AV. The preferred choice of power protection for high performance home entertainment systems, the H Type Power Conditioner combines surge protection, isolated noise filtering, and voltage regulation. Finally, there's a solution that eliminates stress on component power supplies, eradicates EMI/RFI and voltage fluctuation as a source of AV signal degradation, and protects equipment from damaging surges, spikes, voltages fluctuations, and lightning.
See also:
ButtKicker home theater subwoofer - audio connection to the action
Architectural speakers (inwall speakers) - pros and cons
