OT Car Battery Replacement

You can't argue with the fact mechanics use them all the time. Some guys use a "lantern battery" instead of the 9 volt (only 6 volts but a lot "stiffer" and some use a 12 volt "booster pack" ballasted with an

You DO need to leave the doors closed and disconnect the underhood light if so equipped., particularly if using the 9 volt unit.

Ah, that's a good trick! Of course, predicated on the fact that you don't expect anything "of load" to be connected at the time (courtesy light, etc.)

Yes, as I mentioned elsewhere this thread. The problem is,

And when the new 12V car battery is connected, that 9v battery better be removed really fast, or there's a good chance it will explode.

Sure, the voltage is only 3v more, but you're dumping hundreds of amps into that tiny battery.

When 9v batteries are used as backup power in devices such as your home clock radio, they are NOT wired directly into the power supply. They supply power to the clock chip and are isolated from the power suppply with special circuitry. If you post this to one of the electronics newsgroups, I imagine someone could give you an actual schematic.

But be my guest, and blow it up. It's only a one dollar battery and I'm sure no one will die when it blows, but you wont catch me doing it. Having hot battery acid all over the interior of my car is not something I want to clean up. And there is a slight chance it could get hot enoigh to start a fire, if it's touching flammables.

The "ballasted" 12 volt tells you when you mised one.

Nope. Iy has a diode in it. Lets power out, but not in

Nope. Nothing goes back into the battery

It's a simple diode "or gate" Either one or the other supplies power

- whichever has the highest voltage. Any diode will do the job, but a schotky has a lot lower forward voltage drop.

I've done it. I know how. It is 100% safe if done properly

There is no "acid" in a 9 volt battery - that's why it is called an "alkaline dry cell"

Ah! Even cleverer -- the lamp lights! (glows)

The same principal can be used to make the 9 volt battery safe too - a resistance to limit the current drawn from or pumped into the 9 volt battery CAN be used instead of a diode - the real "cheap-assed" units available for the cost of the battery alone could well be using a resistor instead of a diode. The ECU and radio memory only require miliamps of current.

I don't think I ever tried mine, but I wouldn't assume 9v is not enough to retain memory. Not enough to play cassettes but to retain memory is different.

All my chryslers and the 2000 toyoat forget the station presets.

Sorry to hear that.

...snip...

Happens to all of my cars too. Even worse is when you blow them all away by accident.

I was out of town a few weeks ago and trying to find something to listen to on the radio. I was using the scan feature where stations play for about 5 seconds and then move on. If you like the station, you can press scan again (within that 5 seconds) and the head unit stops scanning.

My Honda also has a button that will lock in the strongest local stations, filling up FM1, FM2 and AM. 18 stations in all. That button is right next to the scan button. Guess which button I pressed when "scan" found a station that I liked and I quickly tried to press the scan button to stop the scanning?

Like i said, be my guest and blow the 9v battery up. I'm sure you'll get a thrill out of it. You're right, there is no ACID in it. My bad choice of words, but there are chemicals that will make a big mess. Sure, you can add a diode and will likely prevent blowing up the 9v battery, but that diode will also lower the voltage, which may or may not keep the clock running.

Then again, this whole thread is stupid. How many minutes (or hours) will be spent wiring up the 9v battery with a diode and doing all of this, when it only takes a minute to reset the clock after the car battery is changed. The whole topic is pointless! Change the battery and reset the frikkin clock. DONE!

And on Sunday March 13, 2016 @ 2am, that clock will need to be reset anyhow, when we switch to daylight savings time. Change the battery on Sat March 12, or Sun March 13, and set the clock one hour ahead at that time.

If the OP dont know how to set his car clock, that info is easily avialable online. There's probably even a youtube video about it...

Leave it to Chrysler to do something this stupid........ One reason I only buy GM vehicles....

I'd take one of the old car radios any day that actually had a knob that changed channels and the presets were mechanical and stayed locked in. When I'm driving, my mind is on the road, and there is no 5 second timespan to fiddle around with stupid scan buttons and all of that. With the old radios I could turn the knob and still watch traffic.

Then again, I rarely ever use my car radio. I'd much rather listen to peace and quiet, or in summer hear the birds singing, than listen to some advertiser scream at me..... or hear the mostly crappy music they play these days....

By the way, if you fear losing your radio presets, write them down on a piece of paper. How hard is that?????

You will likely lose any saved fault codes. In California this is a problem if you're about to go for a smog check because the self-tests can take weeks to complete unless you follow the specific drive cycle to complete them quickly.

I had this happen. I went to get a smog check and they said to come back in a few weeks because they could not perform it until the self-tests were complete. If you have an OBD-II Bluetooth dongle, and an Android device, you can buy the Torque Pro program ($4.95) and read the codes.

You don't need much to make a battery "keeper." A 12V battery from a power tool and a diode would do it.

Yes, a 9V battery and a Schottky would work. Or a 12V battery borrowed from a power tool and a silicon diode would also work. Or an 8AA holder

Where would you go to buy one diode now that Radio Shack is gone? In my area I could go to a bunch of places, but I am in Silicon Valley.

True. If you download the detailed instructions for a drive cycle for a specific vehicle it can be completed pretty fast. If you just drive normally it could take weeks to complete.

I ran into this once. Changed the battery just before a smog check and was told to come back in 30 days.

Bad advice.

A 1N914 or 1N4001 diode is probably cheaper than a 1/2 watt resistor, but both wholesale for only a couple of cents so those commercial products could use either.

Take apart damn near any piece of "kit" -- wall wart, lamp dimmer, PC, etc.

Bridge out of a (car) battery charger, alternator, UPS, etc.

Use an LED out of one of those "extra" remotes lying around (you know, the one from that old TV that you discarded 6 years ago), solar landscape light, etc.

It's not the clock. It's the security code on the radio, and possibly the keyless entry too. It's not hard to rig up a memory saver that is perfectly safe. With something as simple as a light bulb to limit the current it is 100% safe. and 9 volts is almost double what is required to hold the memory..

That said, I just changed the battery on my truck and car last week with no memory saver - but the car, the newest of the 2, is 14 years old.

Well, GM does a lot of stupiider things - like producing an engine with the same fatal flaw for something like 12 years - and not just one, either (ignition switch, egr problem in plastic i ntake manifold (3.8 v6) and timing cover problem (3.1) - just for a few....... You can have your GMs. I've had my last one.

I like the sound of a well tuned engine talming through dual 3 inch pipes myself - - -