2007 120i battery repacement

[Clive 0]

Hi,

Any advice on replacing a Din 55 battery with a Din 66 battery ?.On a 2007 120i.

The battery is 2 3/4 years old with no known history, Jap import. 3 months ago.

Alternator is fine, discharge at rest after 40 mins is app 30 milliamps, but battery is

loosing charge at app 4 amps a day !.

I only do 2~3 thousand ks a year ,so car its in garage for up to 2 weeks.

Edited January 15, 2015 by Clive

[B.M.W Ltd 950]

Is the vehicle going into sleep mode ?

[Clive 0]

Clamp meter shows discharge of .03 A after 30 or so mins , is that sleep mode ?.

[kiwi535 538]

i have had HELLA batteries a couple of times,bought from a "battery town" auto electrician.The 120 d had a battery from hell so i am sure there is room for a bigger one than a 55

[hotwire 352]

Get/test the battery properly. If it is infact .03 amp discharge on sleep mode (after about 20 mins) then that is ok. Might be prudent to confirm that with a multi meter. Where are you getting your losing 4 amps a day claim from - how are you coming by that?

Very unusual for an OEM battery to prematurely fail. From what you say - it has already been replaced a few years ago with its second?

That would make two in 7 years. The originals usually last more than that.

If you can phisically fit a bigger battery, (they normally cater for varying sizes) then do so. Bear in mind though - it wont fix an underlying issue, only delay the inevitable. If the car is going to have random use between sitting - it will go flat. I have a garage queen that does exactly that at times.

As Paul says above - Hella Endurant are about the best around if replacement is required.

[Allanw 1071]

Very unusual for an OEM battery to prematurely fail. From what you say - it has already been replaced a few years ago with its second?

That would make two in 7 years. The originals usually last more than that

very true - Our E39 had a battery under warranty in very early 2004 (unusual) - It's still in there now though, very nearly 11 years later.

Dads E30 had it's forst battery replacement after 11 or 12 years too - then another a year later - turns out an alternator fault wasn't charging the battery - the first was probably OK for a bit longer

[Clive 0]

amp discharge a day, based on Trojan Battery guide (USA } this gives % of charge based on volitage at rest after discharging surface charge.

Voltage after 2 days is now 12.47, (78%).

I use Trojan Batterys on my yacht.

[Dave@nz 11]

Hi Clive,

Based on my experience .03 amp draw is okay, you should see minimum of 13.8v to max around 14.5v charging while engine is revving above 1000rpm.

I am not sure on your Trojan guide at all sounds to complicated to me, if intact it was loosing 4 amps per day from no use it would be flat within a few weeks and what that his may be alluding to is with short drives the battery is not recovering the energy lost through the starting process.

What I would do is use one of the modern battery chargers the ones which can do calcium and gell batteries and fully charge it let it sit for a day then work out the trojan table over the following days probably come up with a different figure.

I suspect you may have to purchase a battery tender you are probably not quite using it enough to keep the battery in tip top order.

Dave.

[Clive 0]

Hi, I think I have phrased the question incorrectly.

Thanks for all attempts at help.

The loss of 4 Ahrs a day was arrived at using a multimeter for voltage Plus a derivative of Peukert's Law.

My understaning of a 55 Ahr battery is the rating is based on 20 hrs, ie. 20 hrs at 2.75 A discharge.

Thanks again Clive.