Timm's BMW E31 Safe Battery Replacement The E31 has two 12V batteries connected in parallel. This effectively doubles the available cranking current and capacity but retains the standard 12V voltage. Replacing the batteries on the E31 certainly introduces greater hazards than those found on most other cars with a single battery. The main problems are: If a single battery is changed, both batteries can be destroyed The positive cable can weld itself to the body and upsetting damage will occur The CD changer gets in the way of the RHS battery   The batteries on the E31 are hidden behind the carpeting on the left and right sides of the boot:
It is always best to replace both batteries at the same time. If this is not possible, then it is imperative that both batteries are fully charged. If a new (charged) battery is fitted while a discharged battery is still connected, very large currents will flow and this may damage both batteries. To change the batteries, first fully remove the carpeting over the spare wheel, then remove the left and right covers over the batteries. The left-hand carpeting comes off quite easily. The right-hand carpeting needs to be manhandled over the CD changer and unclipped from the top fixing at the same time. Now remove the NEGATIVE lead from BOTH batteries (even if you are only changing one battery) using the 13mm spanner from the boot-lid tool box. Never disconnect the POSITIVE terminal first, this is unsafe and you may weld your spanner or the terminal to the chassis!
Once the NEGATIVE terminals are disconnected the battery system is safe. Next, remove the CD changer, there is a single fixing, once this is removed (13mm bolt) the changer can be moved forward, removed from the frame and disconnected:
Now remove the CD changer frame, there are two bolts at the bottom and two nuts at the top, all 13mm
Remove the positive terminals on both batteries, remove the vent pipe from the front of each battery. Remove the mechanical fixing (10mm) and remove the batteries from the car:
With both batteries removed, use a mild solution of bicarbonate of soda to clean the area of any battery deposits (the soda will neutralise any vestiges of acid):
FITTING NEW BATTERIES Batteries are normally have two vent holes and a single blanking plug. Fit the blanking plug to the end of the battery with the negative terminal. Start by placing the new batteries in the tray and fitting the clamps, refit the vent pipe elbow and ensure that the blanking plug is fitted at the other end. Re-connect the POSITIVE terminal of each battery, do NOT connect the negative terminal
It is now safe to fit both negative cables. Refit the CD changer:
Refit the carpets and you are done. Time for a cup of tea!
Timm's BMW E31 Safe Battery Replacement The E31 has two 12V batteries connected in parallel. This effectively doubles the available cranking current and capacity but retains the standard 12V voltage. Replacing the batteries on the E31 certainly introduces greater hazards than those found on most other cars with a single battery. The main problems are: If a single battery is changed, both batteries can be destroyed The positive cable can weld itself to the body and upsetting damage will occur The CD changer gets in the way of the RHS battery   The batteries on the E31 are hidden behind the carpeting on the left and right sides of the boot:
It is always best to replace both batteries at the same time. If this is not possible, then it is imperative that both batteries are fully charged. If a new (charged) battery is fitted while a discharged battery is still connected, very large currents will flow and this may damage both batteries. To change the batteries, first fully remove the carpeting over the spare wheel, then remove the left and right covers over the batteries. The left- hand carpeting comes off quite easily. The right-hand carpeting needs to be manhandled over the CD changer and unclipped from the top fixing at the same time. Now remove the NEGATIVE lead from BOTH batteries (even if you are only changing one battery) using the 13mm spanner from the boot-lid tool box. Never disconnect the POSITIVE terminal first, this is unsafe and you may weld your spanner or the terminal to the chassis!
Once the NEGATIVE terminals are disconnected the battery system is safe. Next, remove the CD changer, there is a single fixing, once this is removed (13mm bolt) the changer can be moved forward, removed from the frame and disconnected:
Now remove the CD changer frame, there are two bolts at the bottom and two nuts at the top, all 13mm
Remove the positive terminals on both batteries, remove the vent pipe from the front of each battery. Remove the mechanical fixing (10mm) and remove the batteries from the car:
With both batteries removed, use a mild solution of bicarbonate of soda to clean the area of any battery deposits (the soda will neutralise any vestiges of acid):
FITTING NEW BATTERIES Batteries are normally have two vent holes and a single blanking plug. Fit the blanking plug to the end of the battery with the negative terminal. Start by placing the new batteries in the tray and fitting the clamps, refit the vent pipe elbow and ensure that the blanking plug is fitted at the other end. Re-connect the POSITIVE terminal of each battery, do NOT connect the negative terminal
It is now safe to fit both negative cables. Refit the CD changer:
Refit the carpets and you are done. Time for a cup of tea!