I bought one of those yellow plastic jump start (small suitcase sized jump starter devices for about $ 100 ) a few years ago, it also incorporates a small air compressor and a light).

This year it’s internal batteries failed,  I brought it to a local battery store and they quoted me 120 euro to replace the two small ‘alarm sized batteries’ in it.

Instead I just baught one small ‘Toyota Yaris’ rated battery for approx $60 and fitted it into my small van, then wired it up correctly through a resistor so that it slow charges.

I then wired a bypass heavy hand switch bridging the resistor which when flicked on will connect it to the main battery in parallel as a jump starter.

I secured the auxiliary battery in a space I made under the bonnet.

An auto engineer certificated it and it works fine.

Re: booster box, or portable jump start batteries.

I’ve owned a few of these, and no doubt what I heard sounds spot on. But I’ve got some food for thought.

Ironically, I just had an issue with a car battery last week. The problem was actually me, as I sat in the car while my wife was shopping, and I was listening to the radio and didn’t realize the automatic headlights were on.

Thankfully I have jumper cables in all my vehicles, but I only own one booster box, and it was in my pickup, as I’m frequently way out in the woods with no one around. Being mostly prepared with cables paid off, but my wife and I had to wait for the person parked next to us to return, and thankfully she was willing to help (not everyone is these days), and yes I have roadside, but that day it was going to be hours before they arrived.

I share this story for a multitude of reasons. I’ve never found a booster box I trust completely, as you typically need them in the worst conditions (freezing cold, and when you least expect the need). But my personal opinion is something is better than nothing. My booster is less than 10lbs. Had it been short of power, or just too cold, I can easily carry it to a warm place, and probably get permission to charge it. A car battery is heavy, bulky and requires a specific charger. Not very practical to carry, and good luck finding the nearby place that happens to have a charger.

My point: they’re not perfect, but I think they’re a worthwhile investment. I’ll be ordering two more (one for each vehicle, and one to stay plugged in at the house) and then I will rotate them.

Thanks again jack.

Did I miss the link to the recommended booster?