A different charging cable for starters

Matter of fact, losing battery power more rapidly than usual.

Something's up.

in the phone. I have had an iPhone with a similar problem that was fixed this way.

May help, nay not. But a cheap fix if so.

If it won't charge, maybe there's a malfunction in the battery. There's a place a few miles from here that sells batteries and I had them install a new battery in my phone a month ago. They seemed pretty competent and knowledgeable about all kinds of phones. Take your phone to one of those places and see what they say. If you need a new battery, you can buy it there.

that can replace it under warranty (Apple-store in Denver was waaay too far for me to go at the time). That was the situation with my last iPhone and replacing the battery did the trick.

The problem for me was the the port, the connection was loose in the phone, and I was loosing power.
The guy at Verizon suggested a charging port, which I've used for a year. Got a second one at Walmart, so I carry one and leave one at home. Works great.

Not sure it can be used in a car, but I suggest you try it if your phone is compatible, and if you're not ready to get a new phone. I don't know what an SE phone is.

A soft toothbrush does the trick.

They will clean it at Genius Bar or gently try yourself.

your battery is going.
You can find instructions on how to replace it here. https://www.google.com/search?client=firefox-b-d&q=iphone+se+battery+replacement
Apple will charge you your first born. Better to buy a battery and either replace it yourself from a reliable source like ifixit, or take it to someone who is qualified to replace it.

It’s never been more than $30. The last time I went I thought the better was bad but they checked it and told me it was fine.