I have a '97 Maxima SE that appears to have a parasitic battery drain problem. My wife drives the car short distances, leaves it for several hours, then the engine won't turn over when she tries to start it. I replaced the battery; it worked for a few days before the problem repeated itself.
The battery does appear to be getting charged by the alternator. Measuring AC volts from the alternator, I get about 330 mV of ripple output; I've heard that this should be less than 500 mV, so this reading seems fine. Measuring voltage from the battery while the engine is running, I get about 14V. After shutting off the engine the battery at first reads about 12.5V, then drops slowly, by about 10 mV every 15 seconds or so. About 8 hours after making the 12.5V measurement, the battery reads about 12.1V. If it drops to 11.98V the car won't start.
An ammeter connected in serial with the negative ground cable shows a fluctuating 85-95 mA current with the vehicle shut down, doors closed, etc. I pulled each fuse while checking this leak in order to determine what might be causing it. Removing the BCU fuse drops the leak to about 10 mA. The interior lights and trunk light only add to the baseline drain. When the BCU fuse is left in place, the only fuse from the interior that affects the reading is "Room.L" which drops it to about 75-85 mA. There's also a fuse in the engine compartment, "FL.30A Power Window" that drops it by about 3 mA. Other than that, no other fuses appear to affect the baseline leak.
Is there anything I can do to further diagnose the BCU current drain? Is this amount of drain normal? I've heard that most modern cars shouldn't draw more than 30-50 mA at rest. The car is completely stock with no added electronic components, no phone charger, etc. Are there any components connected to the BCU that I can test? Pulling all the fuses I could find with the BCU fuse in place didn't seem to change anything much; is there anything else I can disconnect?
I know that a faulty alternator diode can cause battery drain, but because most of the drain stops after the BCU fuse is removed, I don't think the alternator is the source. Is it worthwhile having the dealer check the alternator? There is a recall for the alternator on this MY, but I don't think my VIN corresponds to the recalled vehicles.
Any comments or suggestions would be appreciated -- thanks!