2009 Prius - advice for trickle charging / jumping

welcome! driving it doesn't charge it very well. trickle under the hood is fine. if it charges up to 12.5 or better, and holds there, you're good.
if it doesn't get to 12.5, or won't hold there over time, it needs to be replaced. it is possible to get a defective battery, you need to test it.

to test it, measure the voltage under the hood with everything off. then charge it, and wait a few hours after removing the charger for the surface charge to dissipate, and test it again.

 

Get a smart charger in the 3~4 amp range, one that'll run a complete charging gamut on the battery, ending up trickle charging, and can be left on indefinitely, if needed. Also pick up a decent digital multimeter, to measure battery voltage, giving you a rudimentary idea of the battery's state. And just read up a bit on the internet, lots of good info. There's no problem charging the battery at the under the hood jump point, btw.

There's also meters available that'll give you a Cold Cranking Amp status on your battery. Solar BA5 is one example.

This link has a table that outlines what voltage readings will mean. AGM batteries (used in the Prius) tend to be slightly higher:

The 12volt Side of Life (Part 1)

 

who installed the new battery, and what kind is it?
one other thing to check would be the battery terminal connections and the ground wire to body connection. sometimes, when replacing the battery, these connections are not tightened or cleaned properly.

 

it would be a toyota oem then, and under warranty. take it back and have them look at it.

 

One thing that will help a little is if you have SKS key system you can disable it with a button under the steering wheel.
That shuts off all the antenna's amplifier system around the car and will save a tiny bit of power but a Prius sitting for months will kill its 12 volt. Then you use the metal key in your fob. A Prius sitting for days time and time again will kill the little 12 volt battery. A slow loss of 12 volt battery power causes sulphation of the battery.


Look into buying a battery tender with anti-sulphation mode. That will really help.

Should be able to trickle charge from the front jump points no problem. If not your doing something wrong or the battery has already begun sulphation no matter how new it is.

No matter what avoid jump starting a Prius at all costs. Its a quick and easy way to cause big damage to the electronics in the car.
Especially jump starting a Prius stone cold dead 12. If you have to jump it don't have the donor car engine on and never ever use a AAA tow truck.
Buy one of those little jump packs.

Maybe install an RV type battery disconnect switch on the 12 volt? if you hardly drive your car or it sits idle alot a Prius is a poor choice of car. Its problematic in that situation.

 

keep in mind the front jump terminal is metal on one side only.

 

Some clamps it doesn't matter, some it does.

 

ymmv

 

Hi all, I have a 2005 Gen2 Prius, and just found I have a dead 12v, presumably because I left the trunk not well and fully closed.

I have a battery charger (the BLACK+DECKER BM3B Fully Automatic 6V/12V Battery Charger/Maintainer with Cable Clamps and O-Ring Terminals).

So, from the above posts, I gather I can simply trickle charge the 12v from the hood jump points without issue? Anything special I need to know before doing so? And, how will I know if my charger requires both sides of its positive clamp to make contact with metal?

(My Prius is in a garage, and getting the trunk open to access the actual battery is going to be very difficult for reasons I don't need to get into here).

 

There is only a jump point (singular), which is where you make the positive connection, so you need to sort out somewhere to clamp the negative cable. You want to clamp to something "grounded", basically the car body and engine are part of the circuit, the negative side. Which is not hard: a good bet is bare metal on the engine, or any significant (and unpainted) bolt. It should also be secure, no risk of slipping off.

A good way to test is with a multimeter set to Ohms (or continuity if it has it). Put one probe on a bare metal portion of the engine, and touch possible candidates with the other probe. If resistance drops to near-zero (or you get a beep with a continuity meter), you're ok.

Another tester is a a sort-of screw driver with a light bulb, the end is a probe, and it has a wire with alligator clamp running off the handle. Clamp the wire to the positive jump point, then touch the probe to various bare metal candidates. If the light bulb in the handle lights up you're ok to use that point. Here's an example of the latter:

To figure out if your clamp can be used either way, clamp it to something like a piece of wood, then check for continuity between the two jaws.

Trumping all this, if you hook up the charger and doesn't complain, starts charging, you're ok. Just be very careful to always connect positive cable (typically red) to the jump point, and black to ground, not the reverse. Some chargers have safety feature to detect reversed hook up, but not all. So be careful.

 

Thanks Mendel. I've become acquainted with the jump point, as I periodically use a digital multimeter to check the 12v voltage. Pretty sure there's a bolt about a foot north of the fusebox that will serve to attach the black/negative clamp.

And actually there is a light that blinks on the charger when charging is underway. So that alone should tell me if current is flowing into the jump point, right?

 

So... a problem.

My charger won't charge the 12v. Looking in the manual, it says it won't charge a battery that has dropped below 2 Volts. I just read my battery as having 1.96 Volts.

Can anyone suggest a charger that might work here?

 

Called AAA, they jumpstarted at the jump points without a problem. I drove for 45 mins, had to stop for gas, so turned off the car. Car started up again with no problem. Back home now, and the trickle charger is attached and charging properly. I'll leave it charging overnight. So looks like I'm all good.

 

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