The estimate is now 27 million tonnes at 1.06% Li2O for 285,900 tonnes of contained Li2O and includes a maiden indicated and inferred resource for Aldeia of 3.5Mt at 1.3% Li2O.
Savannah said Aldeia's resource was more than 25% higher in overall grade than the project's other previously defined deposits.
The company also upgraded the project's conceptual exploration target to 11-19Mt at 1-1.2% Li2O, giving a potential project mineral inventory range of 38-47Mt.
CEO David Archer said the increase was the fifth major upgrade at Mina do Barroso in just 15 months.
"With the project's development and commissioning targeted for next year, Mina do Barroso is moving closer to meeting its objective of becoming a key strategic supplier of lithium spodumene for the fast-growing European lithium-ion battery and electric vehicle industries - by the year 2025, European lithium-ion batteries are expected to represent a market worth €250 billion (US$278.7 billion) annually.
"Mina do Barroso has the potential to supply circa 40% of the forecast lithium demand from Europe's automotive industry in 2025, and this latest resource and exploration target upgrade supports this potential," he said.
"It is evident that Mina do Barroso could support the development of a mineral conversion plant with the required tonnages of the lithium raw material inputs of spodumene concentrates to act as a base load for a major lithium hydroxide production plant and a new industry for Portugal."
Savannah's shares (AIM:SAV) have had a bumpy 2019 so far, with the current 4.98p (US6.28c) level down from 5.2p at the start of the year and the intra-period peak of 6.5p, but up from the low of 4.7p on February 7.