Hello Everyone!
I own a 1992 Volvo 240. I replaced the Alternator in the car and also bought a new battery. With the car off the battery reads 12.1 and when i start the car its jumps to 12.5. after driving a bit the highest it read was 12.8. I'm not getting any codes or warning lights but this is an issue because i cant drive at night, if i use my lights or anything more, the battery will drain. Any suggestions? Thanks!

 

you should have about 14 V (13.8 to 14.2) when the engine is running, and a fully charged battery should be about 12.6-12.8V at rest.

when you turn on the ignition key, does the BATTERY light (red) come on? when you start the engine, does it go out? both of these must happen for the alternator to work properly.

with a volt meter, test the D+ circuit. Set meter for DC Volts, engine off, ignition on, black probe on an engine ground or the battery - terminal, red probe on the D+ terminal of the alternator, you should see a voltage between 6 and 9V give or take, and that BATT/ALT light on the dashboard should be lit.


Verify the alternator has a good ground, with the engine running, meter in DC Volts, put the black probe on battery - and red probe on a clean/shiny spot on the alternator body, you should read close to 0 volts.

either of these can stop it from properly charging the battery.

 

the tests above can and should be done however i will say i have had both things happen, a bad brand new battery (would not hold a charge) and bad alternators right out of the box. consider returning to your vendor with the parts for bench testing.