Changing alternator

CAUTION
Avoid placing hand in a location where pinching may occur if the holding tool accidentally comes off.

CAUTION
Do not loosen the auto-tensioner pulley bolt. (Do not turn it counterclockwise.) If turned counterclockwise, the complete auto-tensioner must be replaced as a unit, including pulley.

While securely holding the hexagonal part in pulley center of drive belt auto-tensioner, move in the direction of arrow (loosening direction of tensioner) using tool.
Insert a rod approximately 6 mm (0.24 in) in diameter through the rear of tensioner into retaining boss to lock tensioner pulley.
Leave tensioner pulley arm locked until belt is installed again.
Loosen auxiliary drive belt from water pump pulley in sequence, and remove it.

CAUTION
When installing, do not loosen the auto-tensioner pulley bolt. (Do not turn it counterclockwise.) If turned counterclockwise, the complete auto-tensioner must be replaced as a unit, including pulley. Avoid placing hand in a location where pinching may occur if the holding tool accidentally comes off. Confirm belts are completely set on the pulleys.

NOTE
Turn crankshaft pulley clockwise several times to equalize tension between each pulley. Confirm tension of drive belt at indicator (notch on fixed side) is within the possible use range.

To install, reverse removal procedure.

Removal

Disconnect the negative battery terminal.
Remove radiator.
Remove front/right-side engine under cover
Remove the drive belt.
Remove idler pulley.
Remove the generator adjustable top mount, using power tools
Remove the generator lower mount bolt and nuts, using power tools
Remove the generator lower front bracket bolt, using power tools
Disconnect the generator harness connectors.
Slide the generator out and remove.
Installation
To install, reverse the removal procedure.

Removal and Installation
QR25DE
Removal
Disconnect the negative battery terminal.
Remove the front/right-side engine undercover, using power tools.
Remove the drive belt.
Disconnect the generator harness connector.
Disconnect the engine ground wire from top mount.
Remove the generator upper and lower mounting bolts, using power tools.
Set the generator aside and remove the generator top mount.
Slide the generator out and remove.
Fig. 63: Removing Generator Upper And Lower Mounting Bolts
Courtesy of NISSAN MOTOR CO, U.S.A.
Installation
To install, reverse the removal procedure.
Fig. 64: Removal Procedure (QR25DE)
Courtesy of NISSAN MOTOR CO, U.S.A.
VG35DE
Removal
Disconnect the negative battery terminal.
Remove radiator, refer to RADIATOR
Remove front/right-side engine under cover
Remove the drive belt, refer to DRIVE BELTS 2.5L or DRIVE BELTS 3.5L.
Remove idler pulley.
Remove the generator adjustable top mount, using power tools.
Remove the generator lower mount bolt and nuts, using power tools.
Remove the generator lower front bracket bolt, using power tools.
Disconnect the generator harness connectors.
Slide the generator out and remove.
Installation
To install, reverse the removal procedure.

You got a new alternator if its working properly -get the battery load tested to check its condition if okay your problem is coming from somewhere else.