Went out to go start the car this morning, and it was flat, even thought it started fine yesterday.

Its a newish battery, about 4/5 months old.

Ive recently had an amp installed for the front speakers, and an active under seat sub installed, but both of these turn off with the ignition. i also have a usb hard drive in the car, this is constantly powered and doesnt go off with the key.

really it shouldnt go flat if the amps turn of with the key, their power lights turn off so i assume they go off (not got a meter on me)!

Any suggestions as to why its gone flat when it was fine yesterday!

 

duff battery - unlikely if that new
battery not being charged - does it get charged after driving?
something draining battery - most likely.

does it work ok if you disconnect the USB hard drive? as it's constantly connected, it could well be spinning and draining battery. who installed it? shouldn't have something like this running constantly, at least have it on the same circuit as stero (i.e. can only run when stereo is running).

 

Something is draining it with the ignition off.

 

HD uses a constant 12v, cant imagine it being much current, but no point going any further with the investigations until this has been disconected and proved not to be the cause.

I'd put my money on it TBH.

A quick test is jump start the car, then just the lights and sub on, if the alternator is putting no charge in, Your dash will go dim and it will stall after a few mins.

 

Ps take the USB harddrive out you can get 16GB+ USB pen discs on ebay for around 20 notes, they dont need any power.

 

Well i bought a charger and charged it yesterday afternoon, and went out this morning and it started fine! i did unplug the hard drive over night though.

The hard drive is a USB powered one, so i wouldnt have thought that would take to much power to be honest. I've had it plugged in for days before without starting the car and its started fine.

Is there a way i can see if the battery is charging whilst the engine is running?

I installed the hard drive myself, due to it being usb powered it took 2 seconds. the only reason i leave it plugged in, is because it will remember what track i was on before!

 

You can check the alternator by using a multimeter on VDC, with the engine switched off the battery will be around 12 volts and with engine on should be around 13.9 volts.

Did that harddrive have a fan built in?

 

Nope no fan.

Will check the battery tonight, thanks for that!

 

The stock S2000 battery is pants with pants aspects... Suspect it might well be the HDD that is sapping your power

That said, try doing as was discussed above with the volt meter, to determine whether your battery/alternator is stuffed.

The other test to do is to disconnect the negative terminal and use the multimeter (set to Amps DC) between the negative lead and the battery terminal with everything turned off. Then plug in the USB HDD and try again... If you get a significant increase in current flow, you have your culprit.

As a rough guide, your battery will be marked with its capacity in Amp Hours (Ah) or milli Ah (0.001 Ah). If your car is drawing 0.2A and your battery capacity is 20Ah, you can get approx 100h out of the battery without charging it.

 

Flat battery for me too this morning. Only had the car a few days

Is the Halfords one better than dealer? Or are they all rubbish??