2001 740iL Battery Question

[Scolirk]

Hey everyone,

It's been a little while since I've poked around on here. I was bored today and decided to check the battery voltage through the cluster while waiting for my wife to do some shopping. With the car in accessory 1 position, the UB value was between 11.4V and 11.8V, it only went down a little bit when I went to accessory 2 to turn on the fan/air. Kept an eye on it when I turned the car back on and it didn't drop below 9.4V. Cruising the whole way home the car got up to 13.7V but no higher, averaged between 13.2V and 13.7V.

Checked online, Meeknet, e38.org and here for some ideas, seems to be a mixed assortment of answers. I'm not necessarily having any issues but I'm wondering if the batter should be replaced based on these numbers. I can test it in a few hours or tomorrow after sitting to see if those accessory 1 numbers are any lower.

Thanks!

[Grady in Texas]

Don't know the correct value is but how much did it drop while cranking the engine? That an old school test for a weakening battery.

[carnut1947]

You need a battery.

[XAlt]

I've cranked an E39 off a UB of 11.2V and had it running at under 12.5V. Idle with little electronics on should be around 13.6\7 and with everything on a steady 14.

Get a new battery.

[oldroller]

As a rule, a battery with 11.7 volts is considered 50% discharged. When loads are applied, voltage will drop obviously. A good run at 13.8 volts charging should return a healthy battery to 12.4 volts or better resting (no loads).
A drop below 10 volts indicates a weak battery with damaged cells or sulfated plates.
Age and wear/tear on the plates affect the recovery time when charging. An old battery can be charged to hold 12.5 volts resting, but it will not "hold" the charge for very long, as plate efficiency is compromised.
An old battery can perform well enough though struggling, and fail suddenly as plates short or break, leaving you stranded.


If your battery is older than 3 years, and having issues, time for a new one.

[Scolirk]

Thanks for all the replies everyone! I'll call my local shop to see how much a new battery will run me. Maybe it will solve my slight rumble issue at idle.

[Qsilver7]

Why call a shop when its easy to either call or use your device that's connected to the internet and price shop their 49/H8 battery. You'll also need to know to check your battery vent tube set-up to see if you need to get a new little black elbow that facilitates hooking up the car's vent tube to the new battery.

BTW, there are lots of past threads about battery replacement...this topic has been discussed for the last 20 years.

If you require a larger battery for any reason...then the e38 can also handle a 95R/H9 battery class size...you'll have to move the battery hold down clamp all the way to the last hole..but it will fit (and cost more money).

You can see in the East Penn battery chart below...what the average specs (RC/CA/CCA/AH) are for the 49/H8 and 95R/H9 batteries are...batteries made by the other two battery MFGs (Exide & Johnson Controls) will be pretty close in specs. Price and warranty...especially honoring and having a good database to retrieve your warranty info...are some things to consider when buying a replacement battery, too.