With Apple following its usual policy of not disclosing such information in its official specification sheets, the details came from China Telecom, one of China's largest mobile carriers.
Previously, China's telecoms regulatory agency known as the TENAA made its device registration database openly available, which confirmed that the iPhone 11 series would have 4GB of RAM, and now this information regarding the new iPhone SE is also leaking out of China.
In addition to a photo of the second generation iPhone SE, the registered info showed that it features 3GB of RAM, while the detailed specification tab listed a battery capacity of 1821mAh. The stated battery capacity matches that of the iPhone 8 (as per iFixit), and exceeds that of the previous iPhone SE (1624mAh).
The new iPhone SE was rumored to be based on the iPhone 8 while also using Apple's new A13 Bionic SoC processor that is found in the iPhone 11 series. Although the latter rumor was officially confirmed by Apple with the product announcement, it appears likely that the rumor stating the new iPhone SE will reuse multiple parts from the iPhone 8 is true as well.
Apple seems to be hinting at a relationship between battery life and the A13 processor, stating that the "iPhone SE features the industry-leading performance of A13 Bionic that enables great battery life" in its official press release. Furthermore, with the A13's use of machine learning to maximize its energy efficiency, it's possible that the presence of the A13 could lead to improved battery life despite using the same battery as the iPhone 8.
However, Apple lists the same video playback time of up to 13 hours for the previous iPhone SE, iPhone 8, and the new iPhone SE (image from PhoneArena). As such, it's possible that the battery life could end up being pretty much the same across the three devices.
It will be interesting to run some battery life tests on the new iPhone SE once it is finally released.