Have Halfords killed my car?

Imo if your running a car invest in a battery charger. They come in handy for all sorts of things and they can even help partially revive an old battery.

Charge it and see what happens. Monitor the voltage through odb11 and see what it drops to. Anything below 12.5 and get a new battery.

Alternatively just get a new battery.

That’s not saying much. “Battery health check” could just be putting a meter over the terminals and seeing what comes out. A proper health check is a bit more involved.

They have a machine for doing it.  It prints out a little ticket with some blurb, I think it’s probably the same thing I’ve seen at garages.  They don’t necessarily know how to interpret the results though.

They don’t necessarily know how to interpret the results though.

whilst they may not, I’d expect them to err on the side of “lets sell this chap a new battery and make some profit” rather than “this might be ok for another year”. Certainly most national chains are like that when it comes to tread depth, brake pad wear, etc etc

I can bet almost any chain will suggest replacement of battery that isn’t under their warranty if it shows anything a bit low on a test.

I had an elderly battery with an intermittent internal fault, usually fine, sometimes ~2V lower than usual. A new battery is almost always the answer.
Just check that the alternator is working well, if it is going soft the battery doesn’t get the full charge, so cranking voltage drops which means higher current which then burns the starter…
I’ve got a USB plug for the fag lighter which shows battery voltage, after driving enough bangers I like to keep an eye on the voltage these days to get in ahead of the breakdown.

I can bet almost any chain will suggest replacement of battery that isn’t under their warranty if it shows anything a bit low on a test.

Mine came back a bit low on some numbers but he said I’d probably be ok and didn’t sell me anything. He was wrong, as it turned out, but he wasn’t trying to flog me anything.  A bit like when I went to Kwik Fit and specifically asked for an A/C regas but he tested it and told me it was fine and sent me away.