Replacing the 12 volt battery in a 2007 Camry Hybrid

(This was written in December 2013. As of July 2015, I'm still 100% satisfied with the results.)

We don't hear much about 12 volt battery replacement in Camry Hybrids.  After six and a half years I decided it was past time to replace the 12 volt battery in my 2007 even though it wasn't showing any signs of failure.

Previous research indicated the Optima D35 Yellow top battery, part number 8040-218, would be a good choice. More recently, I found the Sears DieHard Platinum, Group Size 34/78DT, model 51090 (a.k.a 50090), which appears to be made by Odyssey. See http://www.odysseybattery.com -  Many prefer Odyssey to Optima and the Sears branded version is available at a lower price then the Odyssey brand. The Optima D35 technically isn't a "reverse terminal" battery but the terminals are not well-placed for our use.  The Sears terminal placement is essentially the same as the original battery.

I was surprised that my local Sears store had a fresh (current month) battery in stock.  I paid $207 plus tax and kept the old battery rather than getting a $15 credit.

There are three installation issues with the Sears battery (and likely with the Optima as well): no hydrogen gas vent tube, no thermal sensor, and somewhat different size.  The gas vent tube on the original battery prevents hydrogen gas buildup in the trunk in overcharge conditions.  Aftermarket batteries don't have this tube-connected vent. From what I've read, the risk of excess hydrogen gas from a sealed battery in the Camry trunk is very small and is commonly ignored.  I agree. While I don't understand the need for the thermal sensor, it may use battery temperature as an indication of overcharging.  I wanted to preserve the sensor.  Lastly, we have to deal with the battery size differences.

Installation steps: (Scroll down for photos.)

  1. Write down your radio station settings as they will be lost when the battery is disconnected.  Most other settings appear to be preserved.  (I decided not to try to use a small battery to preserve the settings in order to eliminate any safety or damage risk this might introduce.) 

  2. Close all the car doors, leaving them unlocked.  Leave the driver's side window down too, just in case there is a problem with re-activating the wireless locking system.

  3. Disconnect the negative battery connection followed by the positive connection. These connections and all mounting bolts are 10 mm.  It was easier to loosen the negative connection with a socket wrench than an open end wrench. If you can't loosen it, you may want to pull the battery out a bit first.

  4. Remove the battery hold-down clamp and pull the battery out far enough to disconnect the wiring harness connector from the temperature sensor socket that connects to the sensor inside the old battery.

  5. Disconnect the thin hose from the battery vent and remove the battery.

  6. Pry off the temperature sensor socket assembly from the old battery casing taking care not to damage the thin black sensor wires leading into the battery.  Peal back the label where the sensor wires enter the battery until you see the white glue (silicone rubber?) over the sensor.  Carefully pry out the glue with a small screwdriver, taking care not to damage the black plastic sensor body.  In my case, the silicone rubber broke apart and separated cleanly from the sensor body.  Set the sensor assembly aside.  We'll install it last so as not to disturb the curing glue.

  7. The new battery is about a quarter or half inch too long to fit in the Camry' steel battery base plate.  Remove the four base plate bolts and bend the ends of the base plate down a bit, spreading out the point of contact with the battery.  I found it essentially impossible to bend the formed steel ends and simply bent the ends at the flat area where they join the base. Bend the base plate ends just enough so that the base plate lays flat on the battery base with little or no end-to-end play.

  8. Reinstall the base plate.

  9. The depression the battery handle fits into is a good place to mount the temperature sensor.  It's as close to the battery cells as we can get and near the middle of the battery top.   Unfortunately, the handle is in the way.  Cut the plastic holding the handle at the hinges and discard the handle.    (I used a cutting disk with a Dremel tool, taking care not to nick or cut any other plastic.)  Later, we'll glue the temperature sensor in the handle storage depression.

  10. Slide in the battery and see that it fits properly on the base. (This is a bit more awkward than you might expect.  Try to hold the back of the battery up as you place it in the base.)

  11. The battery is about 3/4 inch too short for the hold-down clamp.  I cut a 7 inch long piece of  3/4 inch thick, 2 1/2 inch wide (nominal 1 by 3) pine board to use as a spacer.   Using this spacer, adjust the back clamp nut until the front clamp bolt tightens with only enough clamp pressure on the battery to hold it snug. Over tightening risks distorting the battery casing.  Just snug is tight enough.

  12. Plug the temperature sensor into the wiring harness and leave it loose for now.  Connect the positive, then negative battery connections. Leave the trunk open.

  13. At this point, you may want to see if you can get in the car as the wireless remote system has been disabled by disconnecting the battery. The manual says that the wireless remote can be reactivated by pressing the button on a door (locking the doors?), performing a remote operation, or by using the key to open the door. I didn't find it quite that simple and was relieved that after a minute or two of fiddling the system started working. 

  14. With everything working, you can glue the temperature sensor in the battery handle depression.   While the position isn't critical, I found the handle hinge seat on the positive end of the battery to be a good location.  You may want to remove the battery clamp and spacer for slightly easier access and possibly tape down the sensor wire to hold the sensor in position, preferably laying flat on the bottom of the depression. Use a small amount of RTV silicone adhesive flowing under and over the entire sensor.  (Silicone rubber probably has better thermal properties than other glues and has the important benefit of being relatively easy to remove.)

  15. Let the adhesive cure and reinstall the battery clamp if you removed it. You may want to complete the installation by using a wire tie to attach the sensor harness wire to the heavy positive wire.

  16. Enter  your saved radio station settings.