I made the mistake of leaving my bike with the battery in it all winter.  Can I simply charge the battery? Can I use a car to charge the battery? Thanks in advance for your help.

Sure you can charge it up.  I've done it and been OK.  Just bring the battery in and leave it on the charger for a couple days.  Most likely you'll be fine.

couple days???

i brought my battery to my work to charge it...in 2 hours the battery was fully charged and started to expand and got very hot....probobly because the charger is strong of something

you want to "trickle" charge the battery it should take about 8hours or so [usually at a 2amp setting]....if you "fast charge" it it could explode or melt or  who knows what.....Essentialy your just waking the battery up with the trickle charge. I'ts ok to just let it sit all winter but that wouldn't be the ideal situation/storage idea...usually you want to keep them at your std. room temp....but what is done is done

buy a trickle charger you can use a car but make sure it is off or you will fry your battery but even off a car battery is can be too much for your bikes battery and while it won't kill it it could shorten its life.  Trickle chargers are not that much i got my 3 stage one for 25 dollars a 5 stage will cost you around 50
Oh you could also find someone else witha bike to split it with you since you won't need it all the time

OEM battery is 11 amp-hour.  Battery Tender Jr. is 750mA.  If you were starting with a _completely_ discharged battery (like brand new (*)), then it should take over 14 hours... but that's ideal.  In reality, 24 hours would be about right.  Overnight would not be enough.  But really, just leaving a battery dead all winter should still leave some juice in it, so probably overnight is OK.

WalMart sells a similar charger for $15 (1amp) and Sears has one for $20 (1.1A)