Click clunk or clatter. all 3 mean different things but Battery Low Voltage is almost diagnostic
Battery low voltage means either bad battery or battery not being charged properly (Bad alternator). Though it can mean, under some conditions bad connection..
Stories:
On my RV they used commonm "Ring terminals" on the battery positive lead. not proper battery terminals. what is the difference? The metal they are made of. Dissassimular metals even in a very mild acid enviorment quickly corrode (rust in this case) and I had to keep cleaning them. Depending on how bad I'd get a Click, clunk or clatter. Did this every 2 or 3 years till the batteries finally died (Clatter only) then put in new batteries AND A NEW TERMINAL hookup.. Now I have a proper battery connector on that post.
Story 2. Click only, no clunk, no clatter, last summer (13 year old rv) the key operates not the starter solenoid but a pilot relay in the main chassis fuse box.. This makes a sharp CLICK. not the lower pitched CLUNK of the solenoid.
Removed. cleaned contacts. (Cycled manually several times contacts cleaned themselves) replaced. and VAROOM.
Blocking pumps at a PILOT. Cold wet almost freezing drizzle.. Nasty. Late in the day... (Just starting into twilight) I'm tired. and **SSed over other stuff. Not the best conditions for diagnosing an engine problem... But ... Good thing I know my RV.