http://nesdevwiki.org/index.php/NESdevWiki
The rom header will indicate if the game (not just the mapper) supports additional SRAM (mapped to $6000-$7fff). Be careful, some older iNES formats have incorrect headers. You can tell by search for 4 different identifiers in the second half of the $10 byte header. Look at Mednafen's source to see (I don't remember off hand what they were). If the RAM is battery backed, then I'm not entirely sure how to treat the ram when the rom is first ran/encountered. Probably just clear it out. Most(all?) games with battery backed SRAM do a CRC check on power/reset. Dragon Warrior reinitializes SRAM on CRC fail for example.
Also, not all games use VROM. Some games use VRAM (CHR RAM) with MMC and other mappers.