My iRiver HP-120 battery died recently and I replaced it
per these instructions. Removing the old connector and inserting the new connector was a little tricky due to tight clearance, but it snapped in just fine.
I didn't shop around much at all (unusual for me) and picked up a 1450 mAH replacement (v. stock 1300 mAH), with proper polarity connector, for $20. Looks like there are cheaper or higher capacity batteries (though some have connectors with reversed polarity) and I should have done more research before buying to find a higher capacity option. Looks like 1700 mAH batteries are readily available, and I've read 2200 mAH are available, too, but I haven't seen any (nor really looked). At ~10% longer run-times than stock, I'm perfectly happy with my replacement.
Anyway...I'm not quite sure what you're asking. My replacement battery came with the proper cable and plug already connected, so I simply removed the old battery + cable + plug and dropped in the new battery + cable + plug.