Battery flat every few days on a low-mileage hatchback: drain, battery or both?

Does the drain explain it? 340 mA × 24 h = 8.2 Ah per day. A four-year-old 70 Ah AGM testing at 61% of its CCA rating has perhaps 45–50 Ah of real capacity left; usable capacity between full and 50% state of charge is about 23 Ah. That is roughly three days of standing before cranking fails - which matches the customer's history.

Is the drain normal? No. A healthy car sleeps at 20–50 mA. Even allowing for modules still settling, 340 mA is six to ten times too high. The dashcam at 210 mA accounts for about two-thirds of it and is the prime suspect, but 130 mA remains unexplained and must be found.

Is the battery also at fault? It is marginal rather than dead. 12.10 V after 12 hours is around 50–60% state of charge, and 61% conductance indicates age-related degradation. A 12 km commute gives roughly 20 minutes of charging, which barely replaces what the drain removes overnight.

Conclusion: two problems that reinforce each other. Charging voltage is acceptable, so the alternator is not the cause; fixing only the battery or only the drain will bring the vehicle back.

Make the measurement trustworthy. Zero the clamp on a known-zero conductor. Close all doors and the bonnet, latching the catch or using the interior latch so the car believes it is shut. Lock with the remote and wait 45–60 minutes, re-checking every 5 minutes until the current is stable - a still-falling reading means a module is awake and the number is meaningless.

Isolate without waking the network:

• Measure the millivolt drop across fuses with a high-resolution meter and a fuse-resistance chart. This is non-intrusive and does not disturb the vehicle.
• If you pull fuses, bridge the holder with a fused jumper so the circuit never loses supply, then remove the fuse and watch the clamp. If a module wakes, refit everything and wait for sleep again before continuing.
• Work from the largest consumers: the dashcam fuse tap first, then body control, audio, telematics. Check the alternator for a leaky diode - AC ripple of 0.08 V here is acceptable, so it is not the culprit.

Establish a baseline: disconnect the dashcam completely and repeat the sleep test. Above about 50 mA and the residual drain is yours to chase; 20–30 mA means the accessory was the whole story.

Tell him plainly: the battery was replaced, but the cause was never found, so the new battery was discharged in the same way. That is a diagnosis failure, not a battery failure.

Billing: the dashcam is customer-fitted equipment, so removal and rewiring is chargeable. The battery can go back to the supplier for a warranty test, but at 61% conductance and four years old it will probably be judged serviceable - do not promise a free replacement in advance.

Work: remove the hard-wired dashcam supply or fit a voltage-sensing cut-off, repair any residual drain found, then recharge the AGM with a temperature-compensated charger rather than a fast boost. Carry out any battery registration or BMS reset the vehicle requires, otherwise the charging strategy stays calibrated to the old battery and it will be chronically undercharged.

Advice: document the 12 km duty cycle and recommend a monthly long run or a maintenance charger. Without that advice the vehicle returns in five weeks, and the second visit is a complaint rather than a job.