Optima battery finally died after 9 years

My Optima 12v battery finally died after 9 years. Luckily it happened in my driveway. The car started up just fine but after a few seconds the engine died and the whole dashboard lit up like a Christmas tree. There was no clear indication of what was wrong. Everything blinked, flashed and made weird noises until the car slowly died with the ! triangle still on. I opened the battery compartment to find the negative terminal had battery acid power all around it. I thought AGM batteries were gel?? Anyway, that terminal was permanently bonded to the negative cable connector, so much so I had to quite laterally rip the terminal off the battery to get it out. I went to Autozone to buy a new Duralast battery and a battery cable they allegedly said fit for 2010 Prius. However the battery cable was too big for the battery. Apparently gen 3 Prius uses batteries with the smaller JIS "pencil posts" and not the standard bigger SAE posts. So it looks like at this point, I might as well find a used OEM cable rather than paying more for all the necessary adaptors. Anyone else had this problem? How can I prevent this in the future.. grease the post down? I hate to think if this happened elsewhere and not in my own driveway. The car would have had to be towed until the proper cable was found!

I'd post pictures but all it gives me is an error when I try to upload.

 

The car started normally from what I recall. Then the engine quit. That's when everything weird imaginable started happening. I was unable to even turn the car off completely. Pushing the ignition switch a few times I finally got all the blinking lights to go away except for the triangle, which remained on. The car was clearly struggling for power. The power locks sounded VERY weak but still worked at this point. That just confirmed to me it was losing power. About an hour or two later the triangle was still on so I tried the ignition button a few time times. Of course it didn't start but I did finally make that light go out, although there was a faint electrical noise continuously still heard when I left the vehicle.. I had to manually lock it then since power was longer strong enough for the locks. Next morning it was completely dead. I then checked the 12v battery and seen a bunch of fresh battery acid power completely covering the negative terminal, very indicative of a battery going bad. So I pulled it out to replace it. The negative connect was wielded to the post on the battery, impossible to remove, short of tearing the "pencil" terminal right off the battery. If it wasn't actually dead, it is now. I bought a new Duralast AGM waiting to go in. However, it'll be a few days before that happens because I'm waiting on a replacement OEM battery cable (82123-47040) bought off Ebay for $16, which seemingly is the only cable that can support these "pencil" battery posts. My existing cable still has the last battery's neg post still wielded on it, not even a drill could get that loose. lol If this wasn't a 12v battery issue, what else could it possibly have been? Keep in mind, I had just arrived from vacation where the car wasn't driven in over 3 weeks and not driven but maybe twice in the last 6 weeks, if that matters any. Also this happened to be the day after the first freezing night we had in this area. My guess it was on its last leg and the freezing weather combined with lack of use finally did it in?

Also, I noticed a puddle of water in the battery compartment as well. At first I thought maybe that was from the drained battery freezing and it leaked out water? But upon further research, I figured it probably is from leaves building up behind my tail light causing rainwater to leak in. Whether that water is linked to any of this, I'm not sure. But removing the tail light is too complicated process for me to clean all that out. I'll do the best I can with a hose to try to power wash it out and keep the drain plug out when I put in the new battery, just in case. There was no water in the spare tire area. The drain hole is screw sized in the battery compartment, so no mice is going to get through that except maybe baby mice? lol

 

Yeah but what if the car senses the voltage is fine and stops the engine (its a hybrid after all) with a 12v battery that is actually taking its last dying breaths? Once the engine quits, it would lose the voltage coming from the inverter relying only on a battery that's probably putting out very low voltage at that point, not enough to power the circuits properly to restart the engine. Just a thought. Also who knows what effect a dying (or dead) 12v battery would have on the actual voltage seen by the car even if the inverter was trying to put out 13.7 to 14.5v.

 

I did more research and apparently it's not good to leave a Prius or any hybrid for weeks without running it. Mine was left for almost 4 weeks without being started before I got home to try to drive it again. All the electronics, even when off, draws on that 12v battery. Mine was probably almost drained by the time I tried to start it again. And to add insult to injury, the night before it got below freezing, which likely did the already 9 year old battery in. Now I know.. if I leave to go on a trip for a month, especially during winter when it can freeze, I need to disconnect the neg lead to prevent it from draining it for too long.

But the silver lining is at least this got me looking at the battery to notice/fix the wielded neg terminal, along with the water leak back there.

 

I was able to dislodge the broken negative battery terminal off the battery cable by soaking it overnight in a bowl of vinegar mixed with some hydrogen peroxide. It fell right out after that. How I fixed the leak in the battery compartment was by pulling the taillight and cleaning the dirt buildup behind it. Also I sprayed some silicone solution on the seal to make that look as good as new again. The videos on pulling the taillight on a gen 3 Prius make it look easy. It was not! First when pulling it, the clear plastic separated from the housing. I guess it gets weak after 13 years. Also both clips broke, of course. Luckily two nearby Toyota dealerships had these in stock, only one clip at each of course, for $4 a piece.. But that was better than waiting a week (or 2) to buy them off eBay or Amazon for a bag of 25 for $20 or so. I was able to re-seal the casing back together with superglue. Now all is as good as new, with no leak, new battery and the car starts right up!