In this video I troubleshoot a no start issue with the 2012 Subaru Outback 3.6 and end up replacing the negative (ground) battery cables and ultimately upgrade to a larger Group 34 AGM Battery from Odyssey while installing a sturdier steel battery tray.

0:00 Replacing the corroded negative battery cable
4:10 A sturdier battery mount
9:54 Group 34 Battery installation

Parts used:
Odyssey Battery https://amzn.to/3lpOZc5
Steel Battery Tray https://amzn.to/3oV3MO6
Stainless "J-Hook" bolts https://amzn.to/3lu5wvX
Battery Hold-Down https://amzn.to/3iNdaiZ
Battery Cable https://www.oreillyauto.com/detail/c/...
5/16" Stainless Bolts, washers and lock washers (purchased at Lowes)
Blue Loctite https://amzn.to/3BzSaUA
Battery Terminal Corrosion Protectors https://amzn.to/2YzqVey

Over time the corrosion on my ground side of the battery was eating away at the cable causing resistance. It not only damaged the battery cable to the point it needed to be replaced, but it also was damaging the battery. Replacing the ground side of the cable is pretty simple and inexpensive ($30) but you’ll need to carefully separate the old cable from the harness by cutting away electrical tape. Take your time and be very careful not to cut into wires.

For a while I’ve wondered if I could fit a larger format battery. The stock Group 25 battery in these cars provides relatively low cranking amps and has limited reserve capacity. When the Optima 25 battery would not start the car after the cable replacement, I spent several days trying to revive it on the charger to no avail. It occurred to me that this was my chance to test fit a bigger battery that I borrowed from my Jeep XJ, and when it fit my focus shifted to finding a sturdy and affordable way to mount the larger battery. This turned out to be a fair amount of work as it required me to disconnect the washer bottle in order to be able to bolt the new steel battery tray into place from below the car. Overall I feel this is the battery replacement the Subaru Outback deserves, especially if you are using it as a platform for camping or travel.

A similar upgrade may fit other Subaru Outback years, and maybe other Subaru models, do your diligence measuring first if you don’t have a group 34 battery handy you can borrow from another car like I did ;)