Usually, when you buy a new car, its battery doesn’t create any issue. Everything seems fine for the next few years but as time passes by, its performance starts going down. If you play music or use AC too often in the car when it’s not running, there are chances that battery might die down. In such a case, if you have a battery tester, you can reactivate the battery for the time being and avoid any unnecessary trouble.
That said, keeping a tester with you is not necessary but having it in your car always provides an extra layer of safety and security. So, decide yourself and buy a tester whenever you get time.