Why is my new installed battery causing warning light on lexus es 300 year 2000?

Way too many car owners think that the red battery warning light means the battery is bad. WRONG! That red battery light is a warning light that means the battery is not charging. Replace the alternator.

Too many warning lights to know which one you are talking about. If the alternator was boogered up and it wasn't the battery to begin with, then the battery light will stay on until the alternator is replaced. That one light is telling you that all power is coming from the battery, not the alternator.

If you are talking about the battery warning light, get the charging system checked.  If you are talking about the check engine light, get the trouble codes read with a scanner.

What warning light would that be exactly? It has many.  Try again. 

Somebody goofed. Take it back where the battery was installed.

Have a shop read the fault codes.