When to Replace 12V Battery

There's a bolt on the firewall with another grounding wire on it near the fusebox.

 

that's what i use. i don't see the need to go to the other side, it's not like your trying to avoid a spark near the battery.

 

You can use any bare, grounded metal. For small size clamps, or a multi meter probe, I use location #1. If you're using larger jumper cables that might slip off that, there's a shock tower bolt a bit beyond #2.



The outstanding metal tang at right corner of inverter (supporting cable conduit) is also grounded, but I'm a little leery about connecting to it, lol.

 

Yes, avoid using the inverter cover bolts as ground. I've had check hybrid system errors for unexpected ground detected in the past. The error clears, but best to avoid them in the first place.

 

Thank you for the pic and the info!

Posted via the PriusChat mobile app.

 

Being low, shaded, and dense, that battery won't get nearly as hot on a sunny, hot day as the interior does---or as hot as an under-hood battery does in other circumstances.

 

i still think draining it is the biggest issue.

 

My 2015 Prius has 110k miles. The 12v battery just died almost 4 years to the day since I bought the car. No warning - went out to get in the car and it was dark - dead. I replaced the factory battery with the Bosch Group 51 AGM for Prius at PepBoys $146 after 25% online discount. I don't live in a warm climate so getting only 4 years out of the original battery surprised me.

Note - I had no problems with the posts on the Bosch battery and the clamps on my gen3 Prius.

 

And that's exactly the reason for replacing the battery every four years. Sometimes it just dies without warning. Could you stretch it to 5,6, even 7 years? Maybe, maybe not.

But if you think of it as a regular maintenance cost, like an oil change, then you'll be in a position to jump on a deal like the Bosch at PepBoys without having to worry about being stranded somewhere in the middle of nowhere and paying whatever the 24-hour repair shop feels like gouging you for. At $150, the PepBoys battery works out to roughly $38 per year on a four year replacement schedule. If you try to stretch the replacement out to 6 years, you can drop the cost down to $25/year. Is saving $13/year worth buying car starting booster packs and making sure to keep them charged worth it?

 

Good Information

 

The original battery on our '02 Chrysler -- a regular maintenance-free wet-cell battery -- was more than 7 years old when I replaced it just because...

 

had the battery ever been drained inadvertently during the 4 years?

i've never gotten less than 8 years from the oem

 

Protracted down time is tough on 12 volt batteries, there's constant low level drainage.

Ours often sits for multiple days, and now spends more time hooked up to a CTEK 4.3 charger than not. I've wired in the quck-connect, makes it easy. Coming up on 4 years now, still in the pink.

 

I think @Mendel Leisk brings up a good point.

If you take care of your battery and keep it charged with a quality de-sulfating charger, it will last longer. If you are careful, and never run your battery charge to zero, it will last longer. If you protect your battery from extremely hot temperatures, it will last longer.

If, on the other hand, you are someone like me, who forgets sometimes to turn off headlights, and who lives in Atlanta, and who rarely remembers to hook the battery up to a charger, then you might want to use a more frequent replacement schedule.

The big thing to remember is that these batteries can fail without any warning. It's all risk management - how much is it worth to you to go out to your car and have a 100% certainty that it will start when you push the ignition switch? If that's worth a lot, then it makes sense to replace your battery frequently. Could the battery last longer? Probably. But the chances of failure go up with every year of use.

 

We have left our 2012 Gen 3 hatchback parked for up to 2 months at a time, but we were very careful to unplug the Scangauge and use the vehicle setup menu to turn off the SKS and remote door lock systems. Startup requires re-entry with the physical key and putting the key fob right up to the power button for a restart. The 12-volt survived but it appeared to be getting weak after doing this several times over 4 years, so I proactively replaced it.

On our Gen 3, I have used the setup menu to set the auto-lights-off function to turn off the lights immediately at shutdown.
(Small Aircraft ICEs are sparked by dual magnetos to avoid plane engine failure due to 12-volt battery failure. However, the interior lights and the electrically-driven subset of instruments plus the radios die when the 12-volt dies, so flying becomes high stress, particularly if it occurs at night. I carried a small red lens flashlight to hold in my mouth and a backup radio to cope with this situation.)

 

On our 3rd gen I measured milliamps with the car off, it was around 18, with spikes maybe every 5~6 seconds to around 40. I don't think the spikes were the security icon on the dash: it seemed a little more frequent. Not sure though. It would seem a likely suspect.

 

i leave my car sitting 8-10 weeks every winter in an unheated attached garage, no problem.

when people in cooler climates say they only get 4 years out of a 12v, you have to wonder if something else is going on.

 

No....this was the first problem of any kind we've ever had with the car. The 2015 Prius has been 100% flawless.

For other owners who are near or beyond the 4 year mark on the OEM 12v battery, I would recommend investing $30 in a Battery Tender. It's super easy to connect one at the fuse box under the hood, and you'll accomplish 2 goals. Your 12v battery will always be at full charge, and you'll see the increase in recharge times if/when you start to see some degradation. It may save you a major inconvenience.