iPhone won’t charge does the battery need replacing

An iPhone 3GS would most assuredly need a new battery, since the 3GS was released in 2009. But, it's an ancient, obsolete iPhone, which Apple will not offer battery service or support to. The 3GS is truly so out of date, that most apps simply won't even run on it. It would NOT be worth investing 5 cents into at this point. 3G phone service has been turned off in most places in the world, so it won't even operate on most cellular networks either.

Try and see if it wil charge with another charger.

If it is not charging, it might be dead, the iPhone 3GS Is very old