The single cell LiPo batteries (1s) are substantially less voltage than even the 4-cell packs we have traditionally used. The voltage is so low that most of our electronics (receiver/servo/PT) will not function at the voltage provided. Even those that WILL work (an example is the 4-cell specific GTB and Spektrum receiver) the voltage is so low that the servo is very very sluggish.

A booster is an electronic circuit that takes the voltage available from the battery and bumps it up. As an example, the King Hobbies unit I've been using takes any voltage 3.7-4.2 volts input and outputs a steady 5 volts which is enough to power the electronics.

A receiver pack is, anymore, a small capacity 2s LiPo battery that is carried on the car specifically to power the receiver/servo/PT. The down side to this is that this is a second battery that needs to be charged, etc. The 2s LiPo also is generally too high voltage for receivers/servos and have the potential to burn servos out, so a voltage regulator should also be incorporated.

Receiver packs can also be made from 4 or 5 very small NiMH or NiCd cells which eliminates the over-voltage situation but creates (arguably) even more maintenance in addition to the charging regimen that would be required.

Receiver packs are nothing new. Not too long ago before NiMH battery capacities grew to such high numbers as we've seen the last several years folks running 1/12 Mod ran receiver packs because the high current load of the low turn brushed motors could cause voltage in the main pack to drop low enough that the PT wouldn't pick up or the car would steer to one side or the other as the driver applied power when the receiver wasn't getting enough juice, etc.

My own feeling is that adding a receiver pack completely eliminates any and all of the convenience advantage LiPo batteries offer and, in fact, adds complexity to the point of "why bother". I HAVE used the voltage boosters successfully and am convinced they are the way to go.