Dead Battery After Three Days: Sorting a 92 mA Draw
A 2015 pickup with 62,000 miles has a battery replaced eight months ago, and the customer reports a no-crank after the truck sits two to three days. The battery rests at 12.62 V and passes a conductance test at 730 CCA against a 720 CCA rating. Charging voltage is 14.3 V at idle with headlights, blower, and rear defroster on. A parasitic draw test after a 45-minute sleep reads 92 mA; the manufacturer's limit is 50 mA. Pulling fuse F21, which feeds the radio and amplifier, drops the draw to 28 mA. A customer-installed dash camera is hardwired into F21 with an add-a-fuse tap and is configured to record while parked. The customer does not want to remove the camera.
1. Is the 92 mA reading trustworthy, and what conditions could make it falsely high or falsely low?
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Treat 92 mA as a lead, not a verdict, until the test conditions are proven.
Validating a draw test:
- All modules must be asleep. That typically means 30–60 minutes after the last activity, key fob moved well away from the vehicle, doors latched (use the latch or a door switch simulator), hood switch closed, and no scan tool or charger holding a bus awake.
- Use a low-burden clamp meter or a series ammeter with a bypass switch. Breaking the circuit with a meter that has high internal resistance can drop modules out of sleep or, conversely, wake them.
- Re-arming after a fuse pull or meter reconnect often restarts the sleep timer; wait again before you believe the number.
- Battery state of charge matters. A battery at 12.62 V is roughly 80–90% state of charge, not fully charged; top it up and retest so the reading is not distorted.
A falsely low reading is the bigger trap: a module still awake from a door opening can add tens of milliamps, and a not-yet-asleep module can be well over the 50 mA limit and then drop later.
2. The fuse pull isolates F21. How do you determine whether the camera or the radio itself is at fault, and what result would settle it?
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F21 feeds two different loads, so the 64 mA delta only says the problem is on that circuit.
- With the meter still connected and the truck asleep, unplug the dash camera at its own connector (not by pulling the add-a-fuse).
- Wait through the sleep time again and read the draw.
- Drop to about 28 mA, at or under the 50 mA limit: the camera is the source. The radio's residual draw is normal.
- Still near 92 mA: the camera is cleared and the radio or amplifier is holding the bus awake. Continue with module serial data testing.
- Cross-check by pulling the radio's own connector with the camera connected; the difference should isolate cleanly.
Also inspect the add-a-fuse installation. A tap that is partially backed out, back-probed through insulation, or installed in a live-at-all-times cavity is both a draw path and a fire risk. Note the camera was recording in park - that alone can exceed 50 mA.
3. The customer insists the camera stays and works while parked. What do you recommend, and what should you tell them about the battery?
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Maintenance-mode recording is incompatible with a 50 mA budget unless the camera has its own low-voltage shutdown. Options, in order of preference:
- Rewire to an ignition-switched or accessory circuit so the camera stops with the key. Draw returns to normal and the no-crank disappears.
- Use a camera parking-mode harness with a built-in voltage cutoff set at 12.2–12.4 V. It still draws while parked; it just stops before the battery is too flat to crank. That trades a no-crank for a shorter record time, which the customer must agree to in writing.
- Larger battery or a dedicated auxiliary pack only if the customer accepts the cost; do not simply sell a bigger battery to mask a 40–60 mA unapproved load.
Battery advice: this battery has already been deep-discharged repeatedly in eight months. Deep discharge sulfates plates and a conductance test can pass a battery that has lost reserve capacity, so charge it fully, retest, and document that the no-crank is now an installation issue rather than a defect. Make clear in writing that the repair is conditional on the camera circuit being corrected.