A battle rifle is usually defined as a military issue rifle which shoots a full-power cartridge, such as 8mm Mauser, .30-06, or 7.62x51mm. Battle rifles can be bolt-action, or autoloaders. Rifles in this category include the Mauser and Enfield variants, the HK G3, the U.S. M1 Garand, the M14, and the FN FAL.
An assault rifle is usually defined as a select-fire automatic rifle shooting an intermediate cartridge, such as the 8mm Kurz, 7.62x39mm, or 5.56x45mm (a.k.a.223 Remington). Rifles in this category include the StG44, the AK-47 series, the M-16 series, and most current military issue rifles like the FAMAS or the British SA-80.
Semi-auto variants of military assault rifles are *not* properly termed assault rifles. An assault rifle, by definition, is a select-fire weapon capable of full-auto and semi-auto fire. If it can't shoot bursts, it's not an assault rifle, regardless of liberal gun-banner terminology.