DIY report: replace 12v battery with 55ah "ExpertPower" from Ebay

Successful report of replacing the 12v battery on a 2005 Prius with an aftermarket battery from Ebay.

There's a lot of info about different ways to do this in the forums, but no comprehensive tutorial that I could find, so I thought this might be useful to write up.


Battery:
ExpertPower 12v 55ah AGM battery (with internally threaded terminals)
$120 on Ebay from seller "expertbattery"
12 Volt (12V) 55 Amp (55Ah) VRLA AGM Sealed Lead Acid Battery 55 AMPS HIGH CAP | eBay

Note that the photo in the listing has no brand name, while the battery that actually arrived is branded "ExpertPower." Also it says "Non-Spillable Lead Acid Battery" instead of AGM, but my understanding is that these are the same.

This battery was chosen after reading a post by Britprius. Not only is the ExpertPower battery much cheaper than OEM, it's also higher capacity (55ah instead of 45ah) and thus better at handling long slow discharges (although I'm not sure if the battery I got is actually a mobility battery or not). None of the other brand recommendations from previous threads, such as Bosch, were available. The MightyMax battery came up a lot in searches, but the flag terminals seemed more difficult to deal with than internally threaded ones.

Britprius's excellent post:
Fitting mobility 12volt AGM battery. | PriusChat

Also thanks to PriusCamper's recommendations for terminal modifications in this post:
Replace 2005 12 Volt Battery | PriusChat


Other parts:
M6 bolt, 1.00 pitch, 25mm length, hex head, x2
M6 washer, medium size, x4
M6 washer, large size, x1
M6 nut (reused from positive terminal of old battery)
M6 bolt, 1.00 pitch, 35mm length, hex head with washer, x1


Result:
Works great! Plus I instantly gained an extra 2-5 mpg, nice bonus


Instructions:

1. Make sure car is off. Remove trunk lining and black plastic crate underneath. Remove side trim. Now you should have full access to the 12v battery.

2. Remove the brake control power supply (the black box in front of the battery). Unplug all connectors. Remove big vent tube on the left. Remove the black plastic piece on top of the battery where the connectors plugged in. Disconnect both terminals (recommend negative first, then positive, to prevent the chance of a short circuit with a metal tool). Remove old 12v battery.






Old battery and new battery side by side. The new one is slightly taller and slightly wider.




Test fitting: new battery goes into the bottom bracket just fine, despite being bigger.




3. Transfer the negative terminal lead from the old battery to the new one. As PriusCamper suggests, I used two M6 washers to sandwich the lead and then an M6 bolt to screw into the battery.






It may also be possible (I realized later) to turn the negative lead on its side and screw it in directly, without the need for extra washers, as shown in Britprius's post:



4. Attach the top bracket. This is the part that took the longest to figure out. In the end all I did was use a longer screw.

Illustration of the problem:



Since the new battery is taller, the top bracket no longer fits. PriusCamper suggests using a vise clamp (presumably with a hammer) to rebend it. However, I found the rebending process was not ideal. The metal kept twisting so it wasn't square anymore, it looked ugly, and not everyone has a vise clamp at home. And in the end, the rebent bracket still wasn't long enough, so I bent it back to the original shape and went for plan B: just use a longer bolt.

With the M6 35mm bolt in place, the bracket is held tight and there is no wiggle room:






5. Drill a new hole and attach the black plastic piece (where the harness connectors used to be) to the top metal bracket. It attaches with a small plastic clip, but because the new battery is bigger, the original placement is not quite right anymore. To make it align correctly with the positive terminal, I drilled a new hole using a 3/16" drill bit.




6. Attach the positive terminal lead to the battery. I used the same strategy as before, with two M6 washers sandwiching the lead, but with the addition of an extra-large washer on top (because the smaller washer kept slipping) and an M6 nut on the bottom (to make the heights line up correctly). The M6 nut was taken from this same positive terminal lead, since its corresponding bolt was no longer needed.





It may also be possible (I realized later) to combine steps 5 and 6 here by getting rid of the leftmost stack of bolts/washers completely and instead bolting directly like this, as shown in Britprius's post:



All set with the new battery:




7. Time to reconnect all the things. But first, check the orientation of the negative terminal lead (the picture below is correct) to ensure it will screw into the wall properly. Mine was pointing the wrong way, so I had to take out the brake control power supply an extra time to fix it, no biggie.

Reattach big vent tube. Reattach brake control power supply. Plug in all harness connectors. Reattach negative terminal to the chassis.




8. Trim about 3/8" off the legs of the trunk side trim piece, since the battery is now a bit taller. Only 2 of the 3 legs need trimming. Reinstall all trunk trim.




9. Turn on the car. It works! I'm so happy with my new improved mpg too

 

Thanks!!!

Yeah, I'm working on redoing the photos, they showed up fine in the editor but not on post. Obviously not the original thread topic, but if someone could clarify whether this forum supports external file linking, that would be great. Photobucket seems to work, but not PostImage...?

Edit: Go to https://priuschat.com/media/add. Create a new album and upload photos. Right click on each photo to get the image URL. Then in the editing window, click on the button that looks like a mountain and sun, and paste the URL. Now all the links are internal.

 

Do you have a link for these? I looked but couldn't find any.

 

Agreed! I just like the price point better ($120 vs. $230 for OEM) for a car I'll probably only have for a few years. Plus the capacity is bigger (55ah vs. 45ah), so less likely to die if I leave the dome light on for a long time. Better AND cheaper seems like a win-win to me.

(If you have a Gen 3 you'd like to sell, drop me a message...)