A related advancement is handheld car jump-starters have gotten cheap and tiny. They frequently include USB charging ports etc due to those same transistor advancements coupled with improved battery technology.
As long as it has enough charge to do its job when required. What type of batteries are in these, and how long do they hold appropriate charges? I've seen these smaller starters in stores that I immediately dismiss them as useful (dollar stores etc).
I don't know how long the batteries last. I assume they use lithium polymer batteries. Mine I just keep it plugged in all the time.
It’s rarely optimized for in home electronics as people will generally just keep them plugged in. But, when it’s important they are options.