Control LiPo Charging + Constant Re-charging

I have a vehicle-based project that I'm working on (those who know me in the forums have heard about this before). The board will be using an Adafruit FONA (2G) for communications. The FONA requires a LiPo battery to operate, since, when transmitting, it can have spikes around 2A (plus a weird input voltage range).

The FONA has a breakout pin where, instead of micro-USB, you can provide 5V to charge the LiPo.

The board will be running even when the engine is off, but I want to turn off the "charging pin" when the vehicle is off, so that I don't drain the vehicle battery.

So, how can I control the 5V pin that's being used to charge the LiPo? A transistor I'm assuming? What kind? Are there any other components that need to be part of this aspect of the circuit?

Also, if the battery is going to get charged every time the vehicle is running (every day), is that going to rapidly diminish the life of the battery?