Help please, new battery advice

[Mr Tidy]

I replaced the battery in my M in 2021 and don't remember having a problem with it, although I can't remember quite how the cover worked. :roll:

 

[Nick W]

After you've got the battery cover off (three bolts under the foam and compressor) the hardest bit for me was working out how to unclamp the positive terminal connector. I couldn't see how to flip open the plastic cover until I took a photo to post on here and ask how. It was easy once I'd seen what needed doing.

i need this, where is this info?
Pelican Parts have a step by step with photos in their tech articles basic section.

 

[taz1966]

Changed my battery two years ago for a 75AH Bosch none AGM.
I have hade no problems at all.

 

[Mr Tidy]

I fitted an AGM to my MC in 2021 as it looked like it would suit how I used the car better, and it's still performing fine.

E85/86s don't need coding for new batteries thankfully.

 

[Kern47]

So a bit of a long story... But my Z4M died about 4/5 years ago (alternator issue). As a matter of course, I changed the battery first, didn't fix it so I refurbished the alternator. Problem solved.

However I then noticed that, on occasion, the battery light would come on the dash after starting. Without a blip of the throttle, the car would then splutter and die. This was woth the battery brand new.

Then last year, the battery started failing to charge at all. Even hooked up with jump leads to another car, still reading about 12v across the terminals and quickly dying once the leads are removed.

I can't remember what the original battery was that I had, but I suspect it was possibly different to the one I have now, I seem to remember it being smaller in the cage when I fit it too...

Presumably I need to look at a new battery now, perhaps AGM to cure it? The car was limited use, and battery disconnected over winter, so possibly taking a bit of hammering over the last few years, compounding the issue of the incorrect spec ?

 

[Mr Tidy]

The problem is that however young a battery is once it gets significantly discharged it will never be able to hold full charge again.

My car gets limited use, especially over the winter, but my AGM battery still holds charge for a month of inactivity 4 years after fitting. It's a 70Ah Exide, but I think you can get 80Ah that will fit in the cage.