My old S40 won't start and I assumed it was an old battery that needed replaced.  I put in a new one but I'm still having some problems.  It did start for a couple days but now I'm getting a click and it is not turning over.  The lights come on and everything looks pretty normal, than click.  So other than me getting a bad new battery, what else may it be?  Thanks for any insight.

Best regards,

Sure, I let it warm on the tender overnight.  It clicked numerous times then out of nowhere it popped off once.  Then click, click, click.....  My first thought was the solenoid, but I'm not so sure now.  Perhaps I have more than one issue?

Best regards,

Eliminate the variable. KNOW that battery is hot before you try troubleshooting.
Then check connections. You touched it, check it, and the ground on the side of the engine.
Report back and then we will see what the next step is.

You could haul it to O'Reilly's and get them to see if it needs charged, and test it.
Wherever you spend your money, IDK if Wal-Mart will mess with one they didn't sell, but the one here has a truly magnificent charger. I left the key on on the backhoe and sucked it Flat. It was Not new but still had some warranty on it. That machine would hit it with a charge, then load it, charge and load, and it took a couple hours but they saved it.
I have a twenty dollar from Harbor Freight and an old six amp charger, which might be a bit much for a small battery, IDK, but I've tried to do what Wal-Mart did, and saved a couple car batteries.
The battery tester has a voltmeter built in. You can load the battery and see if it rebounds after you let offa the button, does it come up enough?

Batteries, petcock, carburetor,, all of them,, trouble makers...
Good luck

There are two things that click. Understand, it's been over two years since I had one, and I'm not one of the gurus. The decompression solenoid clicks and, of course, the starter solenoid clicks. If you're only hearing one, you can reach under the right side of the tank and put a hand on the decomp and see if that is what you're hearing.
I'm hoping someone who actually knows is reading this and standing by to straighten me out if I'm telling you wrong.

Do you have a voltmeter or test light.?

If you're touching the decomp and you hear the click and feel the decomp engage, you are hearing the decomp.
IDK the time difference between that and the starter solenoid.

You know any neighborhood kids?
It's been a minute but I got recruited to put the fancy intake on a race boat when I was probably 11. The old dude was a mechanic at Ford, but his fingers were just too fat to get the nuts on the studs.
If that is a NoGo, do you have a 1/4" drive extension? Put the socket on put some tape across it and shove the bolt in. You can make it stay in the socket. If you're needing a wobble, I've been known to aim one and tape it to keep the angle I need.

If the bolt has a short length with no threads, that is helpful.
Since you can get close, if you have a deep socket, can you stick the bolt in that and start it?
A dot of superglue,, you can get it to let go.