i just recently changed my battery and all of a sudden the battery light is coming on and my message is saying El power system service ergent im not sure if its the battery or the alternator buy i never had this problem prior to changing the battery also it wont hold its charge i think its my alternator but any advice or input would be appreciated

Had similiar battery problems on my S80 T6 - turns out the OEM battery is too small, and volvo replaced it with a larger capacity one.

If the battery will not hold a charge (discharges quickly when the car is off), that suggests one or more of the rectifier diodes in the alternator have failed. The sustained high current required to charge the new battery may have overheated one of the diodes. I usually charge a new battery with a small battery charger after installing it.

Or, you could simply have received a bad battery. It happens. See if the battery will hold a charge if you remove the negative battery connector while the car is off. If it still discharges, the battery is bad.

It started immediately following changing the battery?

1) Make real sure that the posts are clean and the cables are tightened to the posts securely. CHEAPEST

2) Measure the voltage of the battery before starting the car. Then start the car and measure again. Someone may correct me but it should be approxiamately 12.5 volts with car off and 13.8-14.0 volts with the car running. If it is 13.8-14.0 with the car running it probably isn't the alternator. NEXT CHEAPEST IF YOU HAVE A METER

3) My experience with a 2000 S40 was that the battery posts were not the cleanest. These cars nowadays tend to use lots of battery power and if the connections are not tight and almost perfect the computer will flag something. Cleaning the posts and putting some corrosion preventor on them fixed my problem.


Good Luck

Miker

Good luck... had a similiar problem that the dealer misdiagnosed the first time around. Turned out to be the alternator which was discharging the battery instead of charging it. Big bucks to replace ($600+).