Unplug the battery overnight and see if it drains or holds its charge - If it's drained(draining) in the morning then the battery is bad.
Next check to see if something is draining the battery -
1999 Land Cruiser - What goes here in this opening (Black Rectangle)? There does not seem to be electrical connectors inside.
I can't find anything online. I called a dealer and they said 'nothing'... (jeez! I need an interior detail!)
I just replaced all spark plugs (272k) - I purchased it ('99 LC ) at 225k so I'm not sure when the plugs were last replaced - but most of them were not snug when I went to remove them. I came here to check on it - and now I know why! Thanks!
The brute force method to determine if you need new T's is to grab them and pull on the hoses to see if they break (true story!) Be prepared before you do this. But it is better to find out in your garage than to find out off-road somewhere.