Hello all,

I posted recently about my Prius suddenly failing to start and the general consensus was that it was probably a problem with the 12v battery in the trunk. I called my local dealership and they say that there are two types of Prius backup batteries: The old type (which they aren't even sure they have in stock) costs $130. The service guy said that that would be fine in Florida or something, but that in New England the old type doesn't deal well with the cold weather and that I should really get the new type, which is $450. Yikes.

So first, I wanted to get some advice about whether this is all on the level or if this guy is just trying to sell me the more expensive battery.

Second, I wanted to know if there is an easy way to visually tell which type of battery is currently in my car. According to the auto history I looked up on it before buying the car had only one prior owner who lived in New York, which means that either it's got an old-style battery that has weathered several winters without issues or it's got a new-style battery that still managed to fail. Either way there's reason for me to be concerned.

Finally, we are fairly sure that no lights or anything were left on nor did the alarm go off. It's as though the battery just spontaneously died. Wouldn't that be indicative of a more fundamental problem or can cold weather really just kill the battery like that?

Thanks again!

 

If I remember correctly, it is a 2003 Prius. If so, chances are it is an old style battery. But the easiest approach would be to access the battery compartment and pull it out. The battery is located on the left side behind the felt panel.

There are some round holders with a center pin. To release them, take a pointy object and push the pin in. It will release and you can pull the felt out easily.

Do you have a volt ohm meter? You could measure the voltage quickly and that can tell a lot about the state of battery.

BTW, Wikipedia discusses how a discharged, lead-acid battery can freeze. But if you are willing to replace the battery yourself, they are available.

Good luck!
Bob Wilson

 

where can you get a volt ohm meter? awesome info once again bob

 

Didn't immediately see suppliers in Canada, but here is a US supplier:

$10 plus shipping:
http://www.harborfreight.com/cpi/cta...emnumber=92020

$20 plus shipping:
http://www.harborfreight.com/cpi/cta...emnumber=37772
http://www.harborfreight.com/cpi/cta...emnumber=42397

Could also search on "multimeter"

DAS

 

On volt ohm meters, the rule is pick two from: (1) good, (2) fast, and (3) cheap. For 12 V battery systems and house wiring, an inexpensive, $10-20 unit will be perfectly OK. As for where:

- electronic componet stores (ask an engineer or technician)
- most hardware stores (Lowe's, Home Depot)
- most auto stores (Auto Zone)
- WalMart / Sears
- Radio Shack (you can get better but you can't pay more)

You can spend more but don't go 'nuts'. One desirable feature is 'auto-shutoff' in case you forget to turn it off. However, I also carry a cheap, pocket-sized, volt-ohm meter in my backpack, and one set of spare batteries.

An older engineer, I still like 'meter movement' VOMs but they don't take being dropped very well. However their batteries are used only for resistance measurements and last a very long time. The first hint of a problem is when they corrode and eat the terminals.

Bob Wilson

 

Thanks very much for all the advice. I have a multimeter and will use it to test the battery. If it's dead are you saying that I should definitely replace it with the new-style battery? Is it worth the investment given New England temperatures in winter or is the dealership just trying to sell me something? Is the advantage of the newer battery that it's less likely to freeze because it's bigger or is it something else?

Thanks again!

 

With the multi-meter, you'll need to measure the battery voltage at the terminals. _IF_ you have a battery charger, put the charger on and let it run for an hour. Take the charger off and see if you have any voltage.

13+ V. - all cells are there and battery can probably start the car
12 V. or less - at least one cell is dead, so too is battery, don't fool with it any longer

If it measures at least 13+ V., put the charger on and leave it for a couple of hours and try to start it. Once running, do an errand to 'finish' the charge.

If you don't have a charger but another car and jumper cables BE VERY CAREFUL ABOUT THE POLARITY. Jumper the car for at least 30 minutes. Take the jumpers off and measure the voltage.

When you get home, turn off the car and use the multimeter to measure the current drain from the battery (use the ground!). We need to find out what is draining the battery. If you can disable the 3d party alarm system, do, and retest.

As for the battery, I'll eventually go with the Miata battery because once converted, I'll be able to use any US style battery that fits. BUT I don't have any problem with doing my own work. If you are not comfortable with this type of work, by all means, use Toyota.

As for the Toyota battery options, if the 3d party alarm system is causing the problem, an expensive battery will be just as dead. Go with the cheaper battery and get the root problem solved. I have not seen any references to the Toyota OEM battery being particuarly 'weak'. In fact, ask the service department to check the battery drain and tell you if it is normal.

Bob Wilson

 

Thanks again for the advice!

I've never done this kind of thing before, but this seems like the kind of project one could start with, yes? Do you know of a good website or anything that might walk one through the process of removing/replacing the battery, adapting a miata battery and all that?

Also, I have to admit I'm a bit confused by your comment about using the ground when checking the battery with a multimeter. The multimeter I have, which I've used for testing computer power supplies and such, but never anything like this, just has two prongs: one goes on the positive terminal and one on the negative. Is there a separate cable that's supposed to be used for the ground when dealing with more power or am I misunderstanding you? Electronics is not my strong suit, I'm afraid.

 

It is a good first project but I don't have a good web site to recommend. Have you tried Google?

A good start would be to join one of the Prius specific Yahoo groups. They are full of folks with more experience and collected web pages and files. For example, "Prius Technical Stuff" has been a wealth of wise and sage advice on my projects. I also bought the maintenance manuals, $200, and working on cars is nothing new to me. This photo shows what you will be working with.

If I remember correctly there was a small, easily removable felt 'block' on the left side that can be removed to get access to the battery. I understand the battery can be serviced via this port. However, my project required taking all felt out of the left side.

To remove the battery, you will need a small set of metric wrenches. I used socket wrenches but metric box / open-end wrenches would work too. Although a cresent wrench and/or vice grips could be used, there is a risk of 'rounding' the bolts and nuts.

There are three typical uses for a volt ohm meter: (1) measure voltages, (2) measure resistances, and (3) measure current (amps). Each has a seperate protocol so you need to be careful about the scale used for the particular function.

You have already used the multimeter to read voltage. Just put the scale on the one just above the DC voltage range you are measuring, 14 VDC and put the black on the negitive and the red on the positive. Have you measured the battery voltage? If so, what value did you get?

However current is measured differently. To measure current, the meter has to be put in the circut and the amp scale used. If you try to measure current the same way you measure voltage, it will likly damage the multimeter. The multimeter will look like a short to the battery.

The battery has two posts, a positive and a ground. We _ALWAYS_ take the ground cable off first. If the ground is still connected when working on the B+ circuit, contacting any part of the metal frame could result in a loud, nasty and terribly exciting spark. But we can measure current leakage with the ground cable quite safely.

Let me suggest Google some basic electronics web pages on how to measure current and basic electronics. Make sure you understand the relationship between voltage, current and resistance, Ohm's law.

Also, join one of the Yahoo Prius technical groups so the members can offer more details. It is not uncommon to find Yahoogroup members are better able to explain something that I 'know' and not explain very well. Also, their archives often have photos of what is involved.

The Yahoo vehicle specific groups are good places to discuss 'nuts and bolts' and have excellent archives. Greenhybrid.com is a better web site for relative vehicle performance and the buzz about what is happening.

Bob Wilson

 

For DIY instructions:

http://home.comcast.net/~dldorrance/battery.html

Or just buy the parts readymade:

http://www.elearnaid.com/priusparts.html

I see that Dave Dorrance has now linked to the elearnaid site on his page. Perhaps elearnaid will return the favor?

DAS