12V battery dying every winter

The car is constantly making a low-level demand on the 12 volt battery. Regular, near-daily driving will keep it charged. But regularly sitting idle for up to a week, the battery will not charge enough.

Our situation is similar, albeit not quite as extreme. I use a CTEK 4.3 external battery charger regularly. On any day the car is not being used I will connect it and let it do a full charge regimen (this might take 3~6 hours), then just leave it connected till the car is next used.

My charger came with an extra connector cable for permanent attachment to the car, which I used: it makes for a more secure and convenient connection points. I've connected it where the 12 volt positive cable feeds into the under-the-hood fuse box. Other than that it also has alligator style clips, which can be connected at the jump-start point, also in the under-the-hood fuse box

Left connect like this, it just continues to monitor the battery, and does very low level "maintenance" charging.

For charging like this it is best if you're in an enclosed garage, with access to regular alternating current electricity. Different countries with different voltages, you need to research chargers suitable for your area. You want a "smart" charger, one that assesses the battery, runs a multi-stage charging regimen, then settles down to "maintenance" charging, that can be left on indefinitely. Most will have optional charging methods; read up carefully as to which is most appropriate.

Also, for 2nd generation Prius like yours, the Owner's Manual (North American at least), recommends max. charging rate of 3.5 amperes. In North America the CTEK 3.3 is in that range (I have one of those too, works good), and the 4.3 (my current used one) might be a bit too high. It also cautions "if charging the battery in the vehicle be sure to disconnect the ground cable". I've never followed that advice, no problems.

Oh, I just googled "what country manufactures CTEK chargers", and I think you're in luck.

I'm just going to go out and connect ours now.

 

This might be good:

MXS 3.8

I'm struggling with the language, but guessing it's 3.8 amperes, which is not much above the 3.5 specified in Owner's Manual.

Also, that link "acts up" if I click it, maybe something to do with cookies. It's this:

 

Yes. You NEED a battery tender.

 

Yes. The engineers designing the car assume consider it being used almost daily, and not just short trips. For what's worth 14 kms is not a bad length of trip. But as infrequently as once a week, is not good. There is a constant background drain of approx 20 milliamperes, for the car to maintain memories, be ready to detect the "key" when you approach, and so on.

Our battery is on the charger more than off, and in great shape, over 4 years old. I check with Solar BA5 (electronic load tester) occasionally. Now Solar BA9 is more readily available, and there are many similar testers. Or even just a digital multimeter will give you fairly good idea how it is. Check first thing in morning, with the car off, at the under the hood jump point.

But I'm sure if I didn't have it constantly connected it would be a different story. We drive the car maybe every 3rd day, on average. Sometimes several days in a row, then not for 4 or even more days. And often it's only 4~5 kms drive.

 

if you have sks system there should be an off button under the steering wheel which reduces battery drain

 

Yeah, from North American 2nd generation Owner's Manual (page 33):

 

No but thousands of others HAVE.....and the make or model of car really makes little difference.
The battery slowly loses it's charge when not in use.......and when not fully charged wears out quicker.

There really is no need to buy additional hardware.......except the heaters might be good where you live.
The procedure you used successfully before is fine for the battery itself.

At some point, you probably should check the voltage of the charging system when the car is running but I don't remember many or any reports of that failing.

 

Your original post led me to believe that you already had a battery tender-type charger.
And that is all you really need to keep the battery charged.

Of course, that won't help take the chill off the engine.......but that is a different problem.

The trick here is to keep the charger active as much as possible on the days when the vehicle is NOT used.
30 minutes once or twice per day when not used should be enough to accomplish that.......IF the battery is healthy AND there aren't any other hidden problems.

But I just had a thought: IF you have to move the car TO the outlet to charge and then move it away again after a half hour.......that situation might negate the short charge you are able to put into it.

 

That intermitant power could be troublesome. Not sure.

 

IF......you can connect and disconnect the power without starting the car......then there is nothing "troublesome" about it, not for the car or battery anyway.

Some battery tenders completely remove the charging and then monitor the voltage to know when/if the charging needs to be re-applied.
Same thing as connecting the leads yourself.

 

BUT.....in an earlier post, you indicted that there is a timer on the electrical outlet, only supplying power 30 minutes at a time.
If that still is the case, you are going to need to "push the button" two or three times a day or else your nice new equipment will do NOTHING for you.

 

I do the same thing, but mine is connected directly to the 12 volt battery in the rear.

 

keeping it topped up for 30-60 minutes a day is fine. it's the week long drainage that causes issues.