Cocos2d: how to add anchor points to CCSpriteBatchNode

I am doing some tests with animations in Cocos2D using sprite-sheets. The animation works ok except that the anchor-point is in the center. I need to put it in the bottom. With the code below i am not able to add an anchor-point to my sprites, after quite a few tests.

Would someone nice be able to help me with this?

-(id) init {

    if((self = [super init])) {

        [[CCSpriteFrameCache sharedSpriteFrameCache] addSpriteFramesWithFile:@"ratHammer.plist" textureFile:@"ratHammer.pvr.ccz"];
        CCSpriteBatchNode *spriteSheet = [CCSpriteBatchNode batchNodeWithFile:@"ratHammer.pvr.ccz"];
        [self addChild:spriteSheet];
        NSMutableArray *walkAnimFrames = [NSMutableArray array];
        for (int i = 0; i <= 5 ; ++i) {
            [walkAnimFrames addObject:[[CCSpriteFrameCache sharedSpriteFrameCache] spriteFrameByName:[NSString stringWithFormat:@"ratHammer_anim%d.png", i]]];
    }

    CCAnimation *walkAnim = [CCAnimation animationWithFrames:walkAnimFrames delay:0.1f];

    CGSize winSize = [CCDirector sharedDirector].winSize;
    self.bear = [CCSprite spriteWithSpriteFrameName:@"ratHammer_anim0.png"];        
    _bear.position = ccp(winSize.width/2, winSize.height/2);
    self.walkAction = [CCRepeatForever actionWithAction:
                       [CCAnimate actionWithAnimation:walkAnim restoreOriginalFrame:NO]];
    [_bear runAction:_walkAction];
    [spriteSheet addChild:_bear];


}
return self;

}