The solution was to turn Reversion Mode to No. After that, the backup battery test proceeded perfectly all the way through.
Before I installed 16.7.0, there was no problem with backup battery tests. After 16.7.0, the test would start and appear to run for a few minutes, then I'd get a blank screen with tiny "x" in it, followed by a system reboot.
Dynon suggested:
SETUP MENU > SYSTEM SETUP > SCREEN LAYOUT SETUP > REVERSION MODE ENABLED, change this to NO if it is on YES.
This fix worked. Afterward, I turned the Reversion Mode back to Yes.
Dynon said I was not the only instance, but I don't know how widespread it is.