Yes, it has to be at about 14 volts for BMWs - for coding.

As far as I recall, BMW says that it needs to be around 14.5 V, which is alternator's voltage, which is in turn the nominal voltage in the industry. This charger adjusts to a minimum of 14.2 V even though it says "15", so it works fine for me. I charged multiple cars with it, other bmws, never had a problem. In my opinion, 15V is still safe - car's system is designed to handle a certain range - depending on the conditions of the devices, the climate / season / weather. BUT - if you don't feel confident or safe with this voltage - then don't do it. Try to find something else that can produce the exact recommended voltage.

30 A is good enough to keep voltage from dropping. Just watch out for those power up current spikes, they can trip overcurrent protection and you will be fighting the device to make it stay On.

You can use it for anything that requires your car to be powered on - ignition on situation, without engine running. Coding, programming etc. The bottom line is that you have to provide a constant uninterrupted voltage while doing those things. It's just a power supply, people sell them used, online stores sell them new. Mine came from ebay, i think. This one can run forever, so no limits on how long your project lasts (i think i mentioned active cooling built in). An advice on what?