Jump Starters

Bought a RooBoost Li jump starter. Claimed 18000mAh capacity delivering peak 1500Amp starting current. Can also charge devices via either 5V 2.1A or 5V 3A usb and DC 12V 10A plug. Interesting to note that has a label stating ‘Made in China to ROOBOOST Specs’. So I did a little test charging my phone:
My phone is a pixel 2 which has a 2700mAh battery. Fully charged rooboost first. Phone uses quick charge 3A tech so used RooBoost 3A 5V usb port. Phone was charged from 2% to 95% ie 2511mAh. RooBoost dropped from 100% to 60% ie used 40% of 18000mAh which is 7200mAh. So it appears that Rooboost used 7200mAh to charge a phone by 2511mAh.

Another way of looking at this is to consider 2511mAh as 40% of overall RooBoost capacity which means 100/40x2511=6278mAh. If allow say 80% efficiency we get 100/80x6278=7533mAh total capacity.

This seems extremely poor. Is there a Quality problem? These devices are popping up all over the place and look really nifty as backup starter and device charger for us travelling campers. Could Choice do some serious testing and make recommendations?


Hi Colin

Welcome to the forum and thanks for your detailed information and request

The technical bits are best left to those who understand such things way better than me.

I wanted to let you know that I have moved your post the request a test section of the forum as it appear you are asking for jump starters (you mention "These devices are popping up all over the place") to be tested and reviewed. Please let me know if I have misunderstood you.


Yes these are fairly new compact Lithium battery, automotive jump start devices. There are a range brands with some variety of power specifications which are being advertised across the web eg Ebay, Amazon and also available at both automotive accessory and camping stores.
A test of this specific device would be good but enough around to compare as well.


We’ve had one for quite a few years, but never done a capacity test on it, but it has started our old 2.8litre diesel a few times without any problems.
At very high discharge rates (IE car starting) the efficiency and capacity drops way down, but your test at only a few amps suggests the claimed capacity is no more than wishful thinking by the marketing department.

These devices typically contain 4 X AA or similar size cells. It might surprise some, but a single 2.5Ah AA cell stores enough energy to start a car, but standard batteries will not deliver it at high enough current to do the job. Special construction with large internal surface area is required to obtain a sufficiently high discharge rate.

I’d recommend keeping it solely for car starting duty, and having a separate power bank for charging phones etc when camping. Choice has tested these devices.


This is the Choice website page for power bank tests (Member Content):