There is a vast amount of choice regarding jump starters these days.

With different type of batteries, features and different physical sizes. 

The first thing is to identify what do you need to do with it, what size is practical for you and what is the power required for your purpose.

Knowing that a car battery last between 3 to 4 years it's always safe to have a back up and be able to quickly restart your car.

But you need to find a unit that you can trust when you need it to perform also you should test your car battery to see where you are at.

Features:

They are not only there to replace your car battery in case of breakdown they can also help charging electronic devices when needed and can have other features including :

• Battery charger/ Jump starter
• Compressor for tyre, inflatable or air blower
• Torch/work light
• Inverter
• Voltage/Pressure Gauges
• Fuse protection
• 19 volt output for laptop charging
• Cigarette laptop output
• Power tools charging 

Portable jump starter are a very convenient device to have but how much portable do you want it to be ?

Jump starters type:

As there is different type of unit mainly due to the type of battery and the features included.

Despite the market being crowed with the Mini Lithium power packs which weight between 300 and 800 grams, there is still the Jump Starters with SLA batteries which offer more features like internal compressor, inverters and different types of output USB, cigarette lighter plugs and with more traditional gauges.

The SLA jump starters can weight between 8 to 12 kg and are bigger in size.    

Power:

Regarding the power required for starting a car find below a guide of what on average to expect with the amperage rating:

• Four cylinder petrol/gas – 250-300A
• Six cylinder petrol/gas – 300-450A
• Eight cylinder petrol/gas – 450-600A

Diesel engines require significantly higher cranking currents than petrol/gas engines of the same size, more than two times that of petrol engines, and so guidelines for diesel engines are as follows:

• Four cylinder diesel – 300-400A
• Six cylinder diesel – 400-500A
• Eight cylinder diesel – 600-700A

Jump starter power is more often expressed in Amps and peak Amps some manufacturer use CCA (Cold Cranking Amps).

An other factor to consider when looking at the power required to start a car is how old is your car.

A 20 years old car with 8 cylinders engine would need more power to start. 

Jump starter capacity:

Not to be confused with mAh which is a capacity indicator used to give you an indication on how many times your jump starter can you jump start your car before having to recharge the jump starter (6000 mAh is enough to start most of the car).

Jump starter Safety:

Another point to consider when choosing a jump starter is level of protection the device offer if something goes wrong in the instance of short circuit, incorrect connection or current overload.

This is important for you in order to be safe and that the jump starter or your car doesn't get damage when jump starting.

What to look for:

Finally waranty should be 1 year and the manufacturer or reseller should provide technical assistance.