Battery draining. Alternator has been replaced.

[noctrl]

Hi All,

1996 850 T5 Sedan. Great fun.

I am needing to charge the battery every 2 weeks. Less fun.

The alternator has been changed. Same issue.

When tested with a voltmeter, the voltage stays at 12.6-12.8v instead of climbing as expected.

Light's don't dim to indicate quickly discharging battery. Dash board lights are nice and bright except when trying to start up with low battery

Any advice appreciated in tracing the fault/broken wires.

[rublehousen]

alternator belt slack/slipping?

does the voltage go up when you rev the engine?

possibly your battery is duff. if it has a bad cell then this will be a 'blockage' in the circuit causing a restriction in the amount of charge coming out of the alternator.

either fit a new, or a known good battery and recheck voltage. ORRRRRR if you have a second car and some jumpleads connect leads up as though you are going for a jumpstart, but dont start both cars. just check the voltage in either battery and then start your poorly car up and check voltage again, if alternator is good the voltage will show 13.5-14.5v going into both batteries. (this is just bypassing your duff cell and confirming the alternator is ok, and the battery is the problem. if you still get 12.6v it may be the alternator or wiring issue)

[rublehousen]

also check for loose/corroded terminals on battery, back of the alternator, any earth straps/body earths. and make sure body of alternator has got continuity to engine block. very unlikely but any corrosion on mounting bolt faces will put resistance into the circuit.

[mikealder]

Report back what the battery voltage is to the following:

Engine off (12,3 to 12,7)

Engine running (13,7 to 14,3)

Engine running with all lights, heater blower on full and heated rear screen switched on (12,9 to 13,5)

Figures in brackets are what I would be expecting from a car working correctly - Mike