Lightweight Battery Replacement

Once a BMW starts getting older, one of the common items which require replacement is the battery.  The factory battery, while adequate in all cases, can be expensive (OEM BMW batteries are available only through BMW dealers).

Interstate
A common replacement battery is the Interstate MTP-91, which fits perfectly into most E30 and E36 vehicles' battery compartment.  Interstate batteries is available virtually anywhere, but as a bonus, are slightly lighter than the factory OEM BMW battery.  Because the battery compartment of the E36 is somewhat adjustable, it can accommodate the slightly smaller Interstate replacement.  Expect to pay between $90-100 for this battery.

Performance Distributors
Another option is the Dyna-Batt dry cell battery by Performance Distributors.  Although installation isn't quite as easy, there is a tremendous weight savings.  Some specific issues regarding the installation of the Dyna-Batt include modifying the negative (ground) wire, and using a battery clamp suited for a positive terminal.  For some reason, the Dyna-Batt's positive and negative post terminals are the same size (unlike the BMW and the Interstate).  Retail price is $155 for the top-post version of the Dyna-Batt, direct from Performance Distributors.

From personal experience, this battery has enough cranking power to start the vehicle even in the coldest of temperatures.  For those with large stereo systems or other accessories that require larger-than-normal draws of power, this alternative may not be for you.  When shipped, it has a starting voltage off around 12.5v and when running, can climb to as high as 14v.  In a pinch, you can still jump start the Dyna-Batt battery if you've accidentially drained the voltage from it.

Below are pictures of the Dyna-Batt battery installed in a BMW 330ti Club Sport.  Normally, the battery in a US spec Compact (ti hatchback) is in the engine compartment.  When the E36 M3 3.0L motor was installed, the factory battery was relocated to the hatch area.  By utilizing the storage compartment on the side of the hatch area, the Dyna-Batt fits securely without additional reinforcement or brackets. 

The battery cover pictured was first made from 1/16" thick ABS plastic with cork padding glued to the underside.  The cover was first cut using a jig saw, after fashioning a cardboard sample.  After the ABS plastic was cut to size, a heat gun was used to bend the plastic to form the corners.  The cork material ensures that there is not rattling with the plastic cover contacting the battery terminals.

(click on any picture to enlarge)
Rear Hatch Area	Battery Area	Battery Cover Removed	Installed Battery

Battery Comparison Chart

*According to Performance Distributors, dry cell batteries to not have the same ratings as traditional batteries and thus, does not publish CCA (Cold Cranking Amps) or RC (Reserve Capacity).

As with any traditional battery, it is important to maintain the level of water in the batteries as it can diminish over time.  Without enough water, the battery can run dry, losing it's ability to hold a charge.

Important Links

• Interstate Batteries
• Performance Distributors

Helpful Definitions

• CCA - Cold Cranking Amps - Although batteries may display a CCA number, some may have been tested at higher temperatures so the resulting numbers look higher.  This figure should have been derived from testing at 0º F
• RC - Reserve Capacity - The amount of time a battery can last without a charge.