I wouldnt recommend starting anything with these under 30-50%, it will put much greater stress on the battery and may kill it in short time.I was seeing how long it lasts and the last time it started it with 2% battery!
I posted earlier in the thread about having a noco gb70 which was decent. Update is I've now flogged the gb70 on eBay and got enough to buy a gooloo gt4000 for myself and a gt3000 for the wife's car! Both seem well built, can't tell a difference between them and the noco but the performance is far far far superior. I can't emphasise how much better they are. I appreciate the gt4000 is twice the capacity but it outperforms the noco 5 fold at least!
I'm blown away with the gooloo, I really am!
Other 4000a units possibly will be the same unit with a different name and case, seems to be the way with Chinese stuff on ebay?
In conclusion I wouldn't hesitate to recommend the gt4000 to anyone!