keeping settings when replacing 12 v battery: which booster battery to use?

None. Most modern battery chargers need to see a reasonable voltage level from the battery being charged, before they will produce voltage. The purpose behind this is to ensure that the:

1) battery cables are properly connected and
2) recipient battery is not so dead that it will consume excessive charging current.

Hence, if you feel the need to maintain the various settings, you will need a 12V battery of some sort. It could be a couple of 6V lantern batteries in series. It could be a small 12V battery of the sort used for backup power in alarm systems.

 

Something like #3 will work, since it is a battery. I used a Peak 300 when I did mine. These are handy sources of 12V power, not just for battery jumping and charge maintaining. It is nice to leave in the car at the airport as well, just in case the car battery is DOA upon return.

 

The instructions say "The portable jump starters work great!"

 

OK, if you find that #3 will provide 12V power without requiring other voltage to be present as a prerequisite, then no worries.

 

I connected my combo slow/med/jump start batery charger to the front (underhood) connector on the trickle setting (1A or less), then removed the old battery, and kept all my settings.

 

I want to do the same thing, 2amp/10amp/50ampbooster using the 2amp setting during the swap. I don't have a trickle setting, only the 2amp setting. I use the 10amp setting whenever I want to keep the battery at full charge, the 2amp for trickle which will keep it at around 80/90% of full charge. My Toyota garage suggests using a hot swap. Have you ev er tried this method? [email protected]

 

I used a 0.5 amp trickle charger, old as dirt (so likely not voltage detecting), labelled as being for motorcycle batteries.

There's a lot of commercially available items that consist of a 9 volt battery socket and cigarette socket. Trouble with these, most cars today disconnect the cigarette socket when the ignition is off.

Here's one with gator clips. Still, I've heard a 9 volt might not be enough to hold memory.
http://www.amazon.com/dp/product/B002YKGETA?tag=priuschatcom-20
And this would work, for anyone with a portable jump starter having cigarrete socket outlet:
http://www.amazon.com/dp/product/B002BHX1X8?tag=priuschatcom-20
Plugs between your jumpstarter's cigarrete outlet and obdII on the car. Would just using the starter's jumper cables also work? Or just too cumbersome. I was actually looking for one of these a while back. Nice to see it's available now.

 

The Prius 12V battery is really no harder to change than most other cars. It -may- be a little tighter in there than most under-hood units, but not severely so.

Any small 12V battery will work on the "boost terminal". Just be careful not to hit the brake pedal while you are changing the battery. If you do you could overtax a smaller battery with the 50 Amp brake booster pulse.

NEVER "hot swap" a 12V battery on any car! By "hot swap" I mean with the vehicle on. If you do you are asking to blow very expensive electronics!

 

I used a 12V lantern battery (http://www.amazon.com/Rayovac-926-Lantern-Battery-General/dp/B000ROFZFE) connected to the jump points under the hood as the backup when removing the 12V battery to add water. The lantern battery started out 12.8 something volts. Supplying juice to the car it drooped down to 11 something and going lower with time. Right before I re-connect the 12V battery back it was down to 8 something volts. I thought that was $12 wasted. After the 12V battery was reconnected I quickly checked the ratio stations were still there. I haven't tried to start the car yet. I think a beefier rechargeable 12V battery would be better as the backup.

 

Hello David: I have a battery disconnect switch at my neg. 12V terminal, and have turned it off after car is in ready, as you know the Prius is maybe the only car that this can be done on. And as you know the car can still be driven with no problems. After the drive I have energised the quick disconnect and of course everything is normal. Does this qualify as a "HOT SWAP" ?

 

Are there any crucial setting that should be kept when changing the 12 v battery?
I don't know of any window settings, nor how to turn off the backuo beep
-
The radio I can deal with

Thanks

 

There might also be stored "historical data" that some ECU's use that may have to be re-learned. Some people report that their MPG's are miscalculated for a while after battery disconnect reset. I don't think it's really that bigger deal though.

I just keep an old 12V battery from my other car, it's too weak to crank but still useable for the occasional bench job. I only managed to charge it to about 12.4V but it still held a minimum of 12.3V during the change over.