fix(battery_plus): Incorrect minimum version configuration.

[StanleyCocos]

Description

Since it depends on web ^1.0.0, and web ^1.0.0 has a minimum SDK requirement of 3.4.

• Fix minimum version compatibility configuration.
• Fix documentation errors.

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I titled the PR using Conventional Commits.
• I did not modify the CHANGELOG.md nor the plugin version in pubspec.yaml files.
• All existing and new tests are passing.
• The analyzer (flutter analyze) does not report any problems on my PR.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate that with a ! in the title as explained in Conventional Commits).
• No, this is not a breaking change.