Liquid Acid Battery Refilling

[Curtis135i]

Well, my 2008 135i OEM battery is dying. So after spending some time researching batteries and procedures on replacement..I pulled the battery out and to my surprise it's a liquid acid battery. I assumed it was AGM being located in the trunk. (If I would have looked closer I would have noticed the vent tube)

Someone else also mentioned White cased BMW batteries are Liquid Acid type. And Black ones are AGM.

I inspected the battery and noticed the fill plugs are under the stickers. And the MIN & MAX markings are on the side in the middle.
The liquid was at minimum of course.
So I got the distilled water out, paper funnel, cup and small 2 oz glass to pour in each reservoir. Doing one at a time, I carefully poured water in little by little, making sure not to over fill, but getting the water just right at the MAX level. Each cell took about 3oz of water.

(Must use distilled water only)

A flashlight was handy to see the level through the white plastic. I took a small 3/8" washer and vise-grips to unscrew the caps. (I don't have a 3/4" flat-head screw driver or Phillips that large)

Safety glasses and Latex gloves are very important here. Corrosives are no joke.
Be careful. It is said if you overfill a cell, get some type of syringe and draw it out, putting the liquid in baking soda to be absorbed...for more information or better detailed information, search: how to refill a liquid acid battery.

After charging the battery, then reinstalling, clearing any codes, and driving the car for a day, (200 miles or so) the car has been asleep for 5 days and Voltage is still at 12.6, the same reading when I shut off the car. I'm very happy and confident this OEM battery will last a few more years.

I researched quickly how to refill a Acid battery, and it's pretty straight forward. Not difficult

[NorthernDancer]

Thanks for this-very useful even to someone who has worked with batteries often in his career. My 2008 still has it's original battery tho it sits on a Deltran for 4-5 months each winter. I've often wondered if there is a manufacturing date on a BMW battery; could it be that number (can't see it right now) that ends with DE? Only an expert BMW mechanic might know.

[gjm120]

Originally Posted by NorthernDancer

Thanks for this-very useful even to someone who has worked with batteries often in his career. My 2008 still has it's original battery tho it sits on a Deltran for 4-5 months each winter. I've often wondered if there is a manufacturing date on a BMW battery; could it be that number (can't see it right now) that ends with DE? Only an expert BMW mechanic might know.

No expert here, just a hack. On my original battery (now gone) there was a date code stamped into the neg terminal.

Nearly 12 years on your battery is maybe a record!