Why won't my iPhone 4 hold a charge?

I have an older iphone 4 with no sim card, as i now have a 4s. It hasn't been turned on in a few months, but i decided to charge it and use it. It has been plugged in for about 30 minutes now, and it still only shows the charging thunderbolt on a black screen…

Is it broken?
Any suggestions?
Is it just that low on battery?

Thanks!

It has an old battery, so you should probably get is replaced.

I'm 100% sure but I do know with my iPhone the longer it's been dead the longer it takes to have a charge but idk if it should be that long. Are you sure your charger isn't broken? Haha last time my charger was broken and I was trying to charge it for 40 min.

When it's been off for that length of time and with the battery totally dead, it takes a lot longer to even begin to charge. It may take Nother hour or even two before you see it's retaining the charge.

With it being off so long it will take a long time to recharge. Let it charge over night. The next morning it should be not bad but use it till its dead then recharge it fully again and it will be fine.

Leaving a phone battery completely dead for "months" is not good for the battery. I'm guessing that it will never be the same but charge it a long time and then see.

You can recycle your old phones or ipods on apple's site and they will give you store credit for it, so at least you will get something back for it.
http://www.apple.com/recycling/