State-run Air India says it has started test flights of its Dreamliner fleet with new battery packs and is likely to put them back into service by the end of this month.

The airline stopped flying its six Boeing 787 aircraft in January after Dreamliners were grounded worldwide due to battery fire risk.

Air India said in a statement that the pilots on the first test flight Thursday were satisfied with the plane’s performance.

Since its launch after delays of more than three years, Boeing’s newest jet has been plagued by a series of problems, including overheating of lithium-ion batteries and fuel leaks.

Air India has ordered a total of 27 Dreamliners. Several were delivered last year from Boeing’s 787 campus in North Charleston.