CarTalk.com Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Battery Replacement Question

Hi, all!

I have a 2009 Civic DX that needs the battery replaced. I have an aftermarket Viper keyless entry/alarm system installed, and I’m wondering if I need to worry about reprogramming the device when I change the battery.

The battery has enough juice that I can still use the remote to lock/unlock the vehicle, but I can’t turn the engine over. I want to do a quick swap, but I worry that all of the programming on the Viper brain will be reset. Is this a legitimate concern to where I’d want to find some sort of memory saver solution to use, or am I OK to do a quick swap? I tried Viper customer support, but they were of no help and closed my support ticket without even answering me.

I’m not worried about my car’s clock or radio presets changing at all. I’m just concerned about the alarm system not working properly after I install the new battery.

Thanks for any insight you can provide!

Go to the parts store and purchase one of these.

image

Plug a nine volt battery onto it, and then plug it into the cigarette lighter.

This will prevent all the computers/modules from losing their KAL’s.

Tester

Perfect; thank you very much!

It will not work unless the cig lighter is powered at all times. You could hook up a 9V battery to the battery cables. Be sure to not do anything like open a door and have an extra power demand put on the 9V battery while you do the battery swap.

1 Like

How does that work if the cables have to be removed to replace the battery?

Tester

The car is powered by the 9V battery instead of the car’s 12V battery. Hook up the 9V before you undo cables from the 12V. Move fast and don’t add to its load.

If your power point is not active with the ignition off there are obd options for a memory saver.

1 Like

It only takes a nanosecond of no power for the computers/modules to loose their Keep Alive Memory.

Won’t work.

Tester

No such nanosecond if done in the right order. See above.

Not the most error-proof method, but what I did before was:

  • get a battery (I used an old 12V from UPS) and two long thin wires
  • attach battery to the car battery cables, essentially “back-probing”
  • remove old battery, install new one
  • remove all that contraption

Yes, not ideal, but worked on a couple of occasions

How would I go about doing this? I’m not sure I’m following you.

If it’s not obvious to you, then maybe you shouldn’t do it. If you wire the backup battery backwards, bad things could happen.

Why not just call a few battery places , tell them about your Viper system and see if they install a new battery without causing a problem . If you mess up in your driveway or garage you might have to have the vehicle towed to a shop.

1 Like

There’s a constant power maintainer that plugs into the OBD port and will work even if your cigarette lighter isn’t constant-power.

However, you’ll be fine disconnecting the battery. The first thing a car thief does when dealing with an alarm is disconnect the battery. Alarm makers know this, so they store the programming in non-volatile memory.

Thank you for confirming, and for the explanation, essentially an issue of RAM vs ROM. I appreciate it!

+1

… moreover, Viper is definitely not a no-name brand, most likely it’s gonna be fine

Thank you both for assuaging my fears; much appreciated!

That sounds just fine to me. A 12V car battery is the best possible source of power! A little 9V can do if done carefully.

The 9v battery will work fine, just turn the car off, then turn the KEY to the RUN position. With key in RUN, the “power point” or cigar lighter will be connected, and will give continuous power to the systems. EZ

I would never replace a battery with the key on.

4 Likes