Prostitution is illegal in Indonesia and this includes Batam. Though, as we all know, this doesn't stop it from happening. Though not called prostitutes the preferred term is Bar Girl! The job within the pubs and bars for the bar girl in Batam is to keep the men drinking to increase the sales. They will come and sit with you and chat to you or play pool with you. As soon as your drink gets close to the bottom they will try to get you to have another drink. No responsible service of alcohol here!
The girls will ask you to buy them a drink. If you agree the girls will generally get served a half measure, spirits drink like vodka, Bacardi or bourbon. These drinks are more expensive then if you order one yourself at around 45,000Rp though some of the money does go to the girl.
If the girl agrees you can take them back to your hotel. If you are fat, ugly, old or smelly they will refuse! Most hotels do not have a problem with you taking a non-registered guest back to your room though you do so at your own risk. Check with hotel before you check in if this is your intention. As this is not organised prostitution it is up the girl if they go home with you. If you get along with the girl she may agree to a night of fun though most will ask for payment of around 400,000Rp to stay the night. Some may just ask you to take them shopping the next day though this may cost more and be more annoying in the morning when hung over. If you want the girl to leave the pub before her shift finishes at 1am or 2am then you will have to pay the pub a bar fine to cover any revenue the girl makes in her duties of encouraging drinking. The bar fine can be 120,000 - 150,000Rp. Or the girl may agree to come to your hotel room after her shift finishes.
The girls that work as bar girls in Batam are generally from Sumatra, Java, Kalimantan or West Timor. You sometimes find Chinese girls though they are generally from Sumatra or Kalimantan. Most are un-married mothers who have left their home city to try to support their child. This district in Batam is far more discrete than the equivalent in Bangkok or other parts of Thailand. You may get the girlfriend experience you are looking for but as always 'buyer beware'.