Recharging / replacing 12V battery

My 12V battery came up completely dead this morning. A little surprised as I drove three days ago with no issues, but when I tried to start up all I could get was the "Check Engine" light coming on. The battery is at least 3-4 years old. Would it normally go dead so quickly? I didn't leave any lights on or things like that.

After connecting my portable battery charger for 5+ minutes, all the dash lights come on, but it will not go into Ready (the gear indicator lights and fuel gauge flash repeatedly). Also tried switching my charger to jump start mode (which sends 50 amps) but got the same result.

Just ordered a replacement 12V battery that should arrive Tuesday. I found detailed instructions on AxleAddict about how to replace it, and ordered a multimeter because I'm a dad now and that's the kind of stuff we're supposed to have around

At this point, is it worth trying to recharge the old battery, perhaps to avoid any other issues from sitting with a dead battery too long? Or anything that I should look out for? Thanks!

 

It's a 2005 Prius, 175K miles.

Normally drive 4-6 hours per week, but with the quarantine it sat idle for nearly two weeks. In fact, the parking brake was stuck, so I had to push the parking brake off and on several times to loosen it before I could drive (my driveway is on a slight slope, so I prefer to keep the brake engaged).

Three days before the battery died, I drove about 30 minutes in the city, but it was broken up into a few 10 minute drives. Nothing odd happened, but the short drives may have drained the battery more.

Never used this portable battery charger before on the Prius.

Unfortunately, after letting it recharge for about six hours, I tried to start again and the only dash light to come on was the "Check Engine" light. New battery arrives today, so I'll be able to replace it tomorrow morning. I'll check the voltage on the old battery first (directly from the battery instead of under the hood).

Having read around some other posts here, it sounds like I should have proactively changed this battery as I was approaching the four year mark.

 

Thanks for the tips. The new battery measures 12.6 volts. Looks like that's right where it should be. Since I'm taking the old battery out, any error codes should clear since it won't have a battery for at least several minutes. And I'll hook up my charger just to confirm it shows a full charge. It is a smart charger (Schumacher SE50), charges at 6 amps and switches to maintenance at 2 amps once fully charged (although it says not to leave it this way for an extended period).

Definitely no assembly required of the battery itself... thankfully.

 

Prius manual says to charge at 3.5 amps or less, but my charger will only charge at 6 amps. So hopefully it's got enough juice to start so I can get a lower amp charger.

 

Got the air duct out of the way in order to remove old battery, and discovered battery is sitting in water or acid about an inch deep:


This is the new battery, which doesn't appear to indicate anything about charging amps. Seems it should same or very similar to the old battery though (which does say 3.5 amps).

 

Baking powder fizzes, so it's acid.

Got some advice to get the old battery out and neutralize the acid so I can get it all cleaned out. Gotta work in an hour, so this job won't be done today!

For the record, old battery tested at 7.2 volts after I got it out. Dumped a bunch of baking powder in the acid. I have to work for now, but will check on it soon.

Also, added baking soda to the shopping list. It's obviously no good if it didn't cause any fizzing.

 

Question about recharging the battery. Understand my smart charger should adjust between 6<>2amps, so I don't need to worry about that part. Would you recommend I remove those six caps that are under the battery label?

 

I did have it on the DC setting.

I read elsewhere about removing the caps while charging to allow gasses to escape. Did not want to bother with that, so glad to confirm not to do so!

 

Ah, that explains why there was water in my spare tire space as well. Baking powder is definitely fizzing a lot though, so there's acid in there too. I'll look up that thread!

 

I chatted into AutoZone and they said manufacturer specs do not indicate the max charging amps. Seems like charging between 2-6 amps should be not be an issue.

The old battery is not leaking anything after I removed it. At any rate, going to suction the acid into a glass container of water and check the advice on the other thread about the water leak.