Dead battery

[DonDon]

I work from home and some weeks I will just use the car to go to the local supermarket and back a few times - about 2 miles each way.

I bought the car about 6 weeks ago, and getting to know it (28i), I checked the battery about a week ago. It is 70Ah and registered at 12.6V first thing in the morning, after standing all night. April last year has been written on it by hand - I can't see a manufacturer's date.

A few days ago, the service light came on when I went to start it, but it started OK and I completed my 15 mile journey. It has come on a couple of times since and there is an excessive discharge message (or similar - I can't remember exactly).

Then yesterday, it wouldn't unlock from the remote (I had to use the actual key) and pressing the start button did nothing at all, the alarm started and the wipers came on. I don't yet have a code reader, but one is on order.

The AA guy said the battery's internal resistance is 16 Ohms when it should be between 2 and 4. I turned down his kind offer of a replacement battery for £230.

I put it on a Ctek charger for about 6 hours on the AGM setting and it appeared to complete its tasks and the Go light came on. However, the voltage now says 11.7V and so it looks dead.

I have two questions:

1. If I often do just a few short journeys, can I and should I replace it with an 80Ah one?

2. Is it likely that these short journeys have killed the battery and should I take the wife's car instead?

[smorris_12]

Sounds like its lost a cell.

That's no point buying a larger capacity battery - you can't compensate for not putting enough charge back in each time you use it. If you have Start/Stop, deactivate it each time you go out as each re-start just depletes the battery further. Best solution is to take the long way home and charge it back up that way!

[matsmith749]

Hand written date on the top of the battery means nothing at all TBH - take that with a pinch of salt.

Right now its clearly time to replace the battery, make sure you get it registered to the car also (else it will overcharge it & fail quickly).

Also would be good to get a code reader - save you (or us) guessing.

[DonDon]

Sounds like its lost a cell.

That's no point buying a larger capacity battery - you can't compensate for not putting enough charge back in each time you use it. If you have Start/Stop, deactivate it each time you go out as each re-start just depletes the battery further. Best solution is to take the long way home and charge it back up that way!

Won't a larger battery at least give me more leeway? I am thinking that I will have to get into a routine of charging it regularly, but would a larger capacity allow that to be a bit less frequent? I don't have start/stop.

[tiglon]

Are you able to leave it on a trickle charger when not in use? I would think that should solve the problem once you've changed the battery.

[Zed Baron]

The battery date stamp should be on one of top of one of the terminal posts (week/year), if its over 5 years old I'd be looking at changing the battery. Try Tayna batteries or the Battery group for prices. My E89 is used sparingly and I keep it connected to a trickle charger in the garage.

[Ole gits rule]

I used my zed very rarely and I used to put my trickle charger on there for a least one day per week and never had any issues at all

[smorris_12]

Won't a larger battery at least give me more leeway? I am thinking that I will have to get into a routine of charging it regularly, but would a larger capacity allow that to be a bit less frequent?

Wrong solution. Leaving a lead acid battery mostly flat or over discharging it ruins the capacity. You'd soon burn the extra Ah out of it over standard and, in a year or two it'll be back to the same position of two good starts and it's flat.

Either drive further or get a trickle charger with external connector.

[B21]

It could well be that some of the circuits in the car are not shutting down properly when the car is locked..

Quite common on E89s..a fault code reader would show a DME error in such circumstances

[javis20]

Agree with a previous post, dead cell in battery.

[DonDon]

I have now got ISTA-D and the only code is that the battery was discharged. I put it on the AGM and Recon settings on my CTEK Time To Go charger. I know that recon shouldn't be used for AGM batteries, but I had nothing to lose.

It appears to be OK now; my local tyre and battery centre checked it and gave it a clean bill of health. I will put it on charge regularly.

[flybobbie]

And remember to charge through the bonnet battery posts, so the cars computer knows what's going on.

[DonDon]

Of course. That's where I have attached my CTEK indicator connector.

[matsmith749]

Once fully drained it's likely (as in pretty much certain) that the battery will never be 100% again, and a nice trickle charger is not the answer.

I had this exact dance with an old car back in the day, when I could not be told. I charged it up every weekend. The charger said it was perfect.

But it could not hold capacity, nor could it deliver cranking amps for anything other than the first start.

Take off charger, start perfect. Drive for a couple of hours & park up for the day. Return to a battery that won't start the car.

Lesson learned.

This could be a battery issue or something else electrical in the chain, I would keep looking, or come back here in a few weeks after getting stranded of course!

[flybobbie]

Mat i think that was back in the day a lead acid battery would work for exactly 25 months, fail one month after warranty ran out.
Think about the plates, they might all total up to say 12.5 volts on a volt meter when just charged, but each plate might only hold 10 percent of amps, so first crank, if it cranks, ok, next crank amps all gone.

Anyone brought battery back to life charging with welder?