1 Kings 16:6, 16:8
6 So Baasha slept with his fathers, and was buried in Tirzah: and Elah his son reigned in his stead.
8 In the twenty and sixth year of Asa king of Judah began Elah the son of Baasha to reign over Israel in Tirzah, two years.
2 Chronicles 16:1
1 In the six and thirtieth year of the reign of Asa Baasha king of Israel came up against Judah, and built Ramah, to the intent that he might let none go out or come in to Asa king of Judah.
The issue is how could Baasha come against Asa in Asa's 36th year when Baasha died in Asa's 26th year and his son took over?
The Chronicler has used 36 years as Asa's reign to describe the kingdom that Asa ruled over. It is not describing how long he had been actually reigning the kingdom itself.
How do we know?
We know because the Asa was ruling part of a kingdom that had been newly divided under Jeroboam and Rehoboam. Asa would rule Judah (now the southern kingdom) that had been originally ruled by Rehoboam. Baasha was one of the rulers of the northern kingdom, which was still called Israel.
Rehoboam's reign over Judah was 17 years (1 Kings 14:21), and his son Abijam reigned for 3 years (1 Kings 14:31-15:2). Then, Asa ruled Judah for 41 years, and it's during his reign that the event in question occurs.
That means that the event being described in our "problem passages" where Baasha makes war with Asa took place in the 16th year of the actual reign of King Asa. 20 years since the kingdom divided + 16 of Asa's actual reign = 36 years of the "reign" (kingdom) of Asa.
The Hebrew word מלכות ('malkuwth') translated "reign" can be, and often is, translated "kingdom". It is used 91 times, and translated as "reign" 40 times, and "kingdom" 51 times.
Therefore the event occurred 10 years before Baasha would die. There is no contradiction.
Would "kingdom" be a better translation in 2 Chronicles 16:1? Probably.
Either way, this is simply another instance where the authors of Kings and Chronicles told the story of the same event from 2 slightly different perspectives. There is, as always, no need for the passages to contradict one another.