Battery drain but multi meter shows it doesn't

Question

I have a Honda Prelude 1998 and if the battery is connected (with car off), after 2 days it is mostly drained. If I recharge it and disconnect the battery, it has a good charge even after 10 days (I know it has a good charge because the charger says so when I try to charge it, and also the car starts smoothly).
The battery is around 2.5 years old.
I have followed some instructions on testing a parasitic battery drain and with everything off, the multimeter is showing a drain of 0.02 (with multimeter set on 20A; I guess that's 20mA) which seems normal.
Is there any advice I could get on what to look at next?
Could the battery have a fault that manifests only when the battery is connected (considering the charge stays there for a long time if completely disconnected)?
I will have to do more testing to confirm, but at some point it looked like the multimeter stayed at 0.02 without any change, but after 30-40 seconds it went up to 0.06 without anyone touching anything in the car and then it went back to 0.02

HandyHowie · Answer

Lead acid batteries can be very deceiving about the amount of charge the have stored.
A new battery may be able to provide the current to run a starter motor for several minutes, whereas an old or damaged battery may only be able to run a starter for 10 seconds.  Because the engine starts within those 10 seconds you don’t realise just how poor the battery is.
Drawing those 20mA from the battery for a while can flatten the old battery, leaving it unable to start the engine.
I would suggest first replacing the battery, there may be nothing wrong with your car.
To identify a real drain, you need to start removing fuses one at a time to see if you can identify which circuit is causing the drain.
A drain can also be cause by the alternator, which may require disconnecting the large cable that goes to the alternator from the battery.  Obviously make sure you reconnect everything before trying to use the car.

Battery drain but multi meter shows it doesn't

One Answer

Add your own answers!

Ask a Question