At present, there are mainly two kinds of car jump starter power bank sources on the market, one is lead-acid battery, the other is lithium polymer.
If it is just a spare car on the car, do not have to buy batteries, buy a best car jump starter, the size and weight of the mobile phone is similar to the charge, usually can be charged when charging when the battery, when the car battery without electricity, this guy probably can start the car 4--5 times.
ECU standby power: it means that the ECU still exists power supply when the ignition switch is closed, the usual ECU has several power supplies, some are supplied by the ignition switch (+15), some are provided directly by the battery (+30), that is, the backup power supply.
Principle and function: the ECU of modern car contains a variety of functions, among which a more advanced function is "self-learning" function, which is constantly revised according to the changes of the body (environment).
For example: ignition time, throttle position, fuel injection and so on, the learning parameters are stored in the RAM inside ECU. KAM (one of RAM) is a random memory. In order to preserve these learning data, we need to provide ECU with a backup power to save data.