v3.25.4
Cover
 6 Months Ended
Sep. 30, 2025
Entity Addresses [Line Items]  
Document Type S-1
Amendment Flag false
Entity Registrant Name INTERNATIONAL BATTERY METALS LTD.
Entity Central Index Key 0001786318
Entity Primary SIC Number 1400
Entity Incorporation, State or Country Code A1
Entity Address, Address Line One 6100 Tennyson Parkway
Entity Address, Address Line Two Suite 240
Entity Address, City or Town Plano
Entity Address, State or Province TX
Entity Address, Postal Zip Code 75024
City Area Code (832)
Local Phone Number 683-8839
Entity Filer Category Non-accelerated Filer
Entity Small Business true
Entity Emerging Growth Company true
Elected Not To Use the Extended Transition Period false
Business Contact [Member]  
Entity Addresses [Line Items]  
Entity Address, Address Line One 6100 Tennyson Parkway
Entity Address, Address Line Two Suite 240
Entity Address, City or Town Plano
Entity Address, State or Province TX
Entity Address, Postal Zip Code 75024
City Area Code (832)
Local Phone Number 683-8839
Contact Personnel Name Norma Garcia