Vacation vs auxiliary battery

[gring40]

I understand that if you have to leave the car for several weeks, the small lead-acid gel auxiliary cell may run down, and that shutting off the SKS or pulling the dome switch will help, as the cell is small and just intended to boot up the computer. I've several questions:

1) I know that lead-acid batteries don't "like" to be run down, and function best at full charge, so why does Toyota use one in this application, since it appears to be a very weak link in a solid car?

2) If it is so small, how about jumping a dead battery with several 6V lantern batteries in series through one of the Aux power outlets, instead of going under the hood into the fuse box? Or, use one of those cigarette lighter-to-cigarette lighter jumpers?

3) Anyone know the capacity of that gel cell in Ampere-hours?

Thanks

[eagle33199]

1) since the battery is needed for so little, and there's a decent DC-DC inverter between the HV batteries and the 12V system, i'm guessing the engineers figured a vast majority of the time the battery would be fully charged. honestly, i wish the battery was a regular car battery, as the problem of killing it would decrease, and as an added bonus we could then reliably jump othre cars...

2) Many people have posted that the could jump it with multiple 6V batteries. the problem with the power outlet, however, is that they're turned off (ie disconnected from the battery) when the car is off. so in order for it to work, you'd have to implement an always on mod, which many people have done, for various reasons.

3) sorry, don't know.

[ramarren]

Hmm. I don't know how big the gel-cell in the Prius is or how long it lasts when sitting.

But I know that the gel-cells that I used to replace the old batteries in my Alfa Romeo and motorcycles hold a charge and survive revival far better than any of the wet cells I've used in those vehicles in the past. They often sit for months at a time, fire right up on demand, and charge back to original capacity.

I'm going to be gone for three weeks. I figured I'd shut off the dome light and SKS, and it should be good. Yes? Or do I need to do any further prep?

Godfrey

[huskers]

Mind sat untouched for 3 and a half weeks. Started with no problems.

[David Beale]

I've used gel cell batteries in various outdoor electronics for quite a few years.

My experience is if you discharge them too far and they sulphate (which all lead acid batteries will do when discharged too far), they are more difficult to "recover" than liquid electrolyte batteries. The reason is in a liquid electrolyte battery, you can shake the sulphate loose by vibration and/or hard charging. In a gel cell, the jelly holds it to the plates. Sulphate is an insulator, and when present, it reduces battery capabilities - both charge capacity and current delivery capacity.

The fact you have "sulphated" a battery (any type of lead acid), reduces its' capacity, even if you have managed to "recover" it. You have permenantly used up some of the chemicals that store and deliver electricity. They will lay in the bottom of the cell cavities as lead sulphate. Continued episodes will build up this "debris", and it will eventually touch the bottom of the plates, slowly draining the charge (it's an insulator, but not a very good one). If you measure the battery voltage you'll find it's around 14V when the car is on. If, after 24 hrs of "off" condition, you see 10V, you have a shorted cell, and the battery "will be toast" shortly. In a gel cell battery such as the Prius has, it doesn't settle to the bottom, as the jelly prevents it. It just slowly accumulates on the plates. It can still cause a slow leak if it gets too thick (shorted cell). I've even seen it deform the plates, pushing them together.

The solution is to keep the battery at near full charge. It may be a good idea to add a "battery tender" to your Prius, if you plan to park it unused for months at a time.

Sorry, I don't know the A/Hr capacity of the Prius battery. I do know it's not designed to start cars. Doing so will permenently damage it (loss of life-time). You CAN safely use a cig. lighter charger to charge up another cars' battery. Just make sure your Prius is "on" when you're charging it and disconnect it before starting the other vehicle.

[tochatihu]

The Prius 12 v battery, presumably, does not cost Toyota very much. Weight reduction was also a design goal I guess, so they used a relatively small one. It was originally 28 amp hours, but may be low-30's in the new model. In my 2001 Prius, 2 lantern batteries in series was not a suitable 'helper' but a 7 AH gel cell is. Others have reported jumping success with (NiCd) power packs from cordless tools.

If somebody ever does 'mix n match' with NiMH modules from recycled hybrid main batteries, a small number of those modules might make an interesting substitute for the lead brick.

[jayman]

I can be away for several weeks on business, and used to worry about my Prius. It never actually went dead, but starting last fall the auto lights would turn on in the underground parking and really dim while the coolant pump started. The coolant pump also ran slowly and made a lot of weird noises, almost as if it was cavitating or the valve was jammed.

In Dec I took the battery out and left it hooked up to a VDC Battery Minder that I got at a good price at a surplus/auction place. A month later when I got back, I hooked up the battery and the auto headlights barely flickered when the coolant pump ran.

I'm inclined to side with forum member "C4" - a fellow Canadian - that the Prius 12 v battery is chronically undercharged in most of the Prius cars. That could mean early replacement and a few forum members have already experienced that.

I rigged up a permanent connector to my Prius 12 v battery, and am in the habit of plugging in the battery minder every night. The autolights hardly flicker when I power up, and the coolant pump is smooth and quiet.

Never leave a conventional "trickle" charger plugged in for a long time or you'll boil the battery out and ruin it.

As far as an emergency power source, I keep a Canadian Tire 700 amp boost box in the hatch. So far I've used it several times to boost dead minivans and a pickup, and it works fine for that. I would never offer a boost with the Prius, too much chance of catastrophic $$$ damage to the car

[theorist]

<div class='quotetop'>QUOTE(huskers @ Aug 18 2006, 11:17 AM) [snapback]305316[/snapback]</div>

Mind sat untouched for 3 and a half weeks. Started with no problems.
[/b]

Now that's what I call a vacation. :P

[pagoda113]

I've been gone for twelve weeks at a time before. Turned off the SKS using the button under the steering wheel. Starts up no problem. Just have to remember that the SKS is off after so long.

Nothing technical to add.