Starting battery: maintaing charge during long periods of non-use

[reidhester]

Hi all,

Our Prius is going to be sitting in the garage for about 6 months. I'm going to "turn off" the system before leaving but am concerned that the starting battery will continue to lose power over the course of these many months. So I was thinking of putting a Battery Tender Jr. on it to prevent this from happening.

Does anyone have any experience with doing this or is it even necessary? If it's advisable, what battery tender would work best for this situation. Thanks in advance.

[budput]

For the 2006 Prius, pushing the "make-the-smart-key-dumb" button definitely won't work. Factory advice to dealer who is going to store an inactive car takes two forms: 1-Disconnect neg battery lead from chassis ground, or 2-Go to the jump start terminal in fuse box under hood, undo the 6mmx1.0 nut with a
10mm socket, lift the wire lug off the stud, close the red cover and lay the wire lug on top, close fuse box. 1 requires gymnastics to open trunk lid non-electrically to reconnect battery wire. 2 requires that you carefully avoid shorting this 12 volt point to the chassis. 6 months is a long time, T. don't say how long a disconnected battery will stay charged, but claim that occidental battery chargers shouldn't be connected to this mini-battery. I suspect they would say that when the six months are up you should wake up this minibattery with a Toyota charger, part number etc. etc., and in any case don't charge at over 3 A, and stop when voltage is 12.0 volts (need a digital voltmeter, but they are cheap these days).

[reidhester]

Thanks for the reply!

[budput]

I just had occasion to leave my 2006 Prius in the garage for a week, so I thought I would try disconnecting the 12V battery at the jump start terminal.
Before disconnecting it I measured 12.61V relative to the car frame. As I disconnected I could see a small spark and the battery went to 12.81V. So clearly the battery was powering something, though I hadn't heard the car making any noises. I couldn't figure how to undo a clip that would let me raise the cable lug to top of the red cover, so I put a piece of cardboard in to insulate it from the stud. A week later I measured at the battery cable and found 12.84V. The garage was warmer than when I had done the disconnect. I reconnected the battery and the car ran ok; no trouble with fuel gauge or driver's window control. Have now run a few hundred miles with no ill effects.