Thread: Battery Advice

So quick update.
Opened up the back of the car, and side door so lights came on.
Figured would go and check voltage. Now 12.09v
What the?
Even if I turn the lights off interior only

Sounds like this battery is dead?

Would be under warranty if that new? Is it possible your leaking some where like a winch direct wired to your battery?

IMO voltage fluctuations could cause the systems errors given a blown brake light can cause similar issues.

If your second battery is a deep cycle and main battery a normal battery I would also wonder if the differences are just not comparing apples to apples.

hi Weakestlink,
Yes my secondary is a yellow top AGM. 55ah.
However i had nothing running last night. The AGM stayed full. Now i 100% agree you can't compare..

However with everything turned off.
the crank battery started at 100% (12.7v) after it settled
In the morning it was 12.2 (50-60%)
after opening a single door it dropped to 12.09V (effectively 40-50%)

Where did my 50% of my main cranking battery go overnight?

Thats what has me stumped. I cannot believe the vehicle locked overnight would draw 50ah (or 50% of that battery).

There was absolutely no load on the system at all?

There is load on the battery even when locked, eg the bcu and the suspension ecu. However the voltage drop suggests very little depth of charge with the likely cause being a dying battery. If the battery is disconnected overnight it may show full voltage in the morning but that doesn't prove its ability to charge properly.

My D4 had a 6 hour run to the dealers for its final warranty service after having to be jump-started that morning, only to be told that the battery was a bit down and so needed to be put on a charger for a couple of hours. It wasn't long before I had to replace the battery myself because it was too flat to start the engine after sitting unused for 2 days.

Hi firefox and do you have a battery charger, if so and if you can leave your Disco for a day, try taking the negative terminal off the cranking battery and connecting the battery charger direct to the cranking battery.

This is normally a No-No, connecting to the negative terminal of the cranking battery but leave your bonnet up for a while before you hook-up the charger and you should be safe.

Leave the charger on over night and then remove the charger and just leave the battery as is and see if it looses charge by tomorrow evening, if you can leave it over night again, even better.

If the battery voltage has dropped again, then the battery is the problem.

If the battery seems to be holding it’s voltage, reconnect up the negative lead again and measure the voltage on the battery terminals and see if the battery voltage drops quickly over the next hour or so.

As Graeme posted, measuring the terminal voltage is not always a good indicator of the true state of your batteries charge level.

If the battery seems to be holding it’s charge once the neg terminal is back in place, it would be more than likely a problem with something in the disco drawing power when it should not be.

Now this next suggestion is an extreme one but do you have a Smart Power meter fitted to your house. I have already had one customer who had problems caused by these meters.

Hi
I recently had my battery replaced by the dealer and while under warranty (just!) was still keen to know if it was due to the electronic disco wizardry draining the battery.

I haven't done it yet but you can measure battery drain with a multimeter to see what current (amps) is being drawn from the cranking battery while engine is off and car has 'shut down'. I'd google to check but my understanding is that you remove the positive from the cranking battery and place a multimeter set to mA in series between the positive cable and positive battery terminal.

I'm sure people on hear have done this and can possibly comment on what a concerning reading would be.

Good luck!

I seem to recall the normal all shut down amp draw is less than a half amp.

It is hard to measure as one has to have the hood up and that means the hook latch's are unlatched which keeps the alarm awake.

With a screwdriver shaft, I forced the hook latch's closed with the hood open.

I discovered that my overhead DVD player with the TV screen was not shutting down - screen continued to glow hours with the lid shut and hours later.

I put a switch in the DVD circuit and that solved the battery drain concern.

I also understand that a defective rear hatch switch can also lead to excessive draw.