35is Battery Replace

tiglon · Post by **tiglon** » Sun Mar 19, 2023 12:55 pm

I've suspected I need a new battery for a while, a couple of times when the car has gone in for work they've said the battery was low and have put it on to charge, and it's been on trickle charger for the past couple of months but never gets up to 80%.

On Friday after updating the map with MHD, the warning late came on for hill start not working - I'm guessing it's due to the battery, is that something that will clear once I change the battery, or will I need a software update?

New Bosch battery is on its way (only £140 from batterygroup.co.uk as opposed to £270 from Eurocarparts etc, for identical battery!) and is the same spec as the original BMW labelled battery, 760a 70ah. Am I right in thinking that it will only need registering, which I can do with MHD, and not coding?

B21 · Post by **B21** » Sun Mar 19, 2023 1:38 pm

Hill start is a DCS function releasing the normal brakes not parking brake…once a battery is low all sorts of s**t can happen..

MHD doesn’t do registering…you’ll need a Protool, Carly type product or a bespoke OBD programmer like Foxwell..

tiglon · Post by **tiglon** » Sun Mar 19, 2023 1:41 pm

B21 wrote: ↑Sun Mar 19, 2023 1:38 pm Hill start is a DCS function releasing the normal brakes not parking brake…once a battery is low all sorts of s**t can happen..

MHD doesn’t do registering…you’ll need a Protool, Carly type product or a bespoke OBD programmer like Foxwell..

On the "codes" tab, under "reset adaptations" there's an option for registering the battery.

B21 · Post by **B21** » Sun Mar 19, 2023 2:09 pm

tiglon wrote: ↑Sun Mar 19, 2023 1:41 pm
B21 wrote: ↑Sun Mar 19, 2023 1:38 pm Hill start is a DCS function releasing the normal brakes not parking brake…once a battery is low all sorts of s**t can happen..

MHD doesn’t do registering…you’ll need a Protool, Carly type product or a bespoke OBD programmer like Foxwell..
On the "codes" tab, under "reset adaptations" there's an option for registering the battery.

Well I just checked..you are right

Must have added that in since I first looked..

MHD just gets keeping better ..

tiglon · Post by **tiglon** » Sun Mar 19, 2023 2:15 pm

B21 wrote: ↑Sun Mar 19, 2023 2:09 pm
tiglon wrote: ↑Sun Mar 19, 2023 1:41 pm
B21 wrote: ↑Sun Mar 19, 2023 1:38 pm Hill start is a DCS function releasing the normal brakes not parking brake…once a battery is low all sorts of s**t can happen..

MHD doesn’t do registering…you’ll need a Protool, Carly type product or a bespoke OBD programmer like Foxwell..
On the "codes" tab, under "reset adaptations" there's an option for registering the battery.
Well I just checked..you are right

Must have added that in since I first looked..

MHD just gets keeping better ..

Yeah they've added a few things since I last checked. For N54 there's now antilag, switchable maps (I think just for different fuel types, rather than different stages or other settings, unfortunately) and a few other random bits I'd never heard of.

flybobbie · Post by **flybobbie** » Mon Mar 20, 2023 8:38 am

I'm surprised the 35is doesn't have the 80AHr battery.

When i inquired about adding software for servotronic which i assume all 35is have as std. i was told needed to upgrade the alternator and battery to 80AHr.

I was looking to improve the steering feel.

B21 · Post by **B21** » Mon Mar 20, 2023 3:44 pm

I can never work out the logic on the 70ah vs 80ah fitment..

My 35is had 70ah as standard..I did put an 80 ah in.

FWIW the E89 uses special current management logic to ensure the EPS always has enough power come what may..so battery capacity in this case is not directly relevant…unless your alternator fails..

Kevin · Post by **Kevin** » Mon Mar 20, 2023 4:56 pm

B21 wrote: ↑Mon Mar 20, 2023 3:44 pm I can never work out the logic on the 70ah vs 80ah fitment..

An 80Ah should deliver the power for a bit longer, but that wouldn't matter once the engine is running.
It might have a higher CCA, which could be what is being recommended, and it's just a coincidence that the Ah is higher?
I wouldn't have thought the extra electronics etc. would make any real difference to the power draw. A 6 might be harder
to crank than a 4 perhaps?

For comparison, my other car is a diesel, which has a higher Ah/CCA battery than the petrol equivalent (and it needs to be AGM since
it has stop-start)

B21 · Post by **B21** » Mon Mar 20, 2023 11:49 pm

Kevin wrote: ↑Mon Mar 20, 2023 4:56 pm
B21 wrote: ↑Mon Mar 20, 2023 3:44 pm I can never work out the logic on the 70ah vs 80ah fitment..
An 80Ah should deliver the power for a bit longer, but that wouldn't matter once the engine is running.
It might have a higher CCA, which could be what is being recommended, and it's just a coincidence that the Ah is higher?
I wouldn't have thought the extra electronics etc. would make any real difference to the power draw. A 6 might be harder
to crank than a 4 perhaps?

For comparison, my other car is a diesel, which has a higher Ah/CCA battery than the petrol equivalent (and it needs to be AGM since
it has stop-start)

I’ve looked at many VINs that have been decoded and failed to see the causal link between options and battery size..given the alternator is rated at 230 amps once the engine is running you’ve got 2.5 kwatts of juice..

The main pros for a bigger battery are longer time to allow car draining it’s electrics on standby, better chance of start in ultra low temps, more reserve capacity for regenerative braking..listen to sound system longer without engine running , plus extended use of blow by heating..

tiglon · Post by **tiglon** » Wed Mar 22, 2023 11:19 pm

FYI, the battery registration function on MHD hasn't worked for me. "Failed" every time. Maybe I should read the manual....

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