SKS non-responsive for a few minutes

The interference I am speaking of would be like having change in your pocket with your fob, or a cellphone in the same pocket. Things like that. Also, the location of the fob vs the receivers on the car. If you stand beside the door the fob will generally work, but sometimes if you stand behind it like towards the back door the fob might give you trouble. I have a feeling it is going to end up being the 12 volt, but before I invested in that I would go buy a brand new CR2032 battery and put it in the key fob and see if that helps. The fob battery is a LOT cheaper than the 12 volt and easier to put in too.

It is well known that a weak 12 volt can cause problems with the key fob range, and it seems that the problem you are experiencing is due to the location (range) of the fob to the car.

Hope all of this makes sense. You are not the first to have this sort of problem. If I get in a bad place and not have my body in the right place, I too will on rare occasion have to touch the door handle twice. Plus if I have my cellphone or a bunch of change around my fob, it will act up at times. It was a lot worse before I changed my 12 volt battery. I was getting 12.1 and 11.9 on my readings when mine was acting up a lot like yours is now.

 

Yes, the whole system works together in tandem. It all works off of a radio signal. The fob can be working great, but if the 12 volt is weak, then the receiver won't always pick up the signal. It doesn't matter if it is the SKS or the buttons, it is still running off of the same radio signal.

With time, the 12 volt has progressively gotten weaker, hence more of the problem you are experiencing. Try a new fob battery. If that doesn't work, then replace the 12 volt. The MFD test will tell you for sure if the battery is on its way out. So far, your numbers are lower than where they should be. Remember mine was acting up at 12.1 volts and that is where you are now. Once I changed the 12 volt, all the problems went away. I had more than one thing going on at that time.

 

My understanding is that the latest Optima Yellow Top is a direct drop in replacement which requires no modification. If you went with that, you would have to revert back to the original configuration of the terminals. I believe the older yellow top used a kit of some sort. Also the new Yellow Top does have the JIS posts (small ones) and they are reversed which is identical to the OEM battery.

I did see a mention of something you referred to, but I was unsure exactly what you were referring to.

I am aware that the Battery Minder I have is supposed to desulfate a battery, however when you read all of the information that the manufacturer provides, it is clear that it takes quite a bit of time and depending on how bad the sulfation has become, there is the possibility that it won't work entirely on a heavily sulfated battery. It is unfortunate that batteries such as these will sulfate over time.

I am not sure if you were referring to something like this, but I thought I would mention it.

On another note, the chart below will give you an idea of what voltages mean concerning amount of charge in your battery. Your battery is a AGM type. Remember that the voltages referred to are measured at the battery terminals in a open circuit with a digital volt meter. In the Prius, the voltage will read about .2 to .4 lower due to draw on the battery by onboard devices.

 

Since you have now seen that the battery won't hold a charge as evidenced by the 12 hour period, I think you are on the right track now.

Many here on this board including myself regularly top off the 12 volt with a good smart charger. If you get into that practice, you may find that the new battery will hold up better over the long haul. The battery in our Prius is 10 months old now. I have topped it off about four times now with the Battery Minder I have. It usually only takes a few minutes to bring it up to full charge.

Our Prius sits at times for two or three days as I don't commute daily to a job any more. Since I leave the SKS system on all of the time, I have to keep an eye on the voltage. I don't want it drop a lot since wild swings in voltage can contribute to the sulfation process.

The product you linked would work great if you were running it on a alternative power source. I believe it basically does the same thing that ours does. The difference I think is the power source. Mine runs on 120 volts. I bought it originally to try to revive the old battery. I nursed it for seven months before finally deciding to change it on a cold rainy morning last January. Glad I have a carport to work under.

Whatever you do, make sure the battery you get is fully charged before you install it. Check the voltage at the post's before you hook it up. Remember that a fully charged AGM type battery should read at least 12.9 volts. Optima should read 13.1 as well as the Toyota True Start.

 

I think the whole idea behind it is to keep the sulfation down to a minimum. All of these batteries tend to sulfate over time. That is one of the reasons they have to be replaced. If you keep the battery fully charged, then the process is slower but it still happens with time. Because of that there are some here on PC that hook up smart chargers at least once a month. The Prius doesn't have the greatest charging system in the world, and it seems that the smart chargers do a better job at topping it off.

Sulfation and How to Prevent it - Battery University

http://www.iceking.ca/_mndata/iceking/uploaded_files/Sulfated%20Batteries.pdf

 

I added a couple of links you can read that goes into the details about sulfation. It is one of those things that "the jury is still out on", but makes a lot of sense. I have looked inside a few dead battery and have seen the crystals they talk about. I have also seen what a shorted out cell looks like. What seems common more than anything is that the batteries were left untended for a long time (allowed to discharge) and or were not kept fully charged.

By topping them off once a month, it stands to reason that the longevity of the battery life will improve rather than get shorter.

 

What kind of electrical noise environment are you in? Cell phones in the pocket can interfere, as can other radio sources nearby. Does this problem happen only in one place, or anywhere?

 

That is weird. The only other thing is the prox/SKS sensors in the car. I've never seen them go bad. Are you able to duplicate this problem at will or does it happen randomly?

 

The dealer should be able to diagnose/fix it but, I personally don't have a lot of faith in them. If they tell you they know what the problem is and want to replace "blank", ask them that if you allow them to replace "blank" will they guarantee you that will fix it? If they say no, walk away. (that's my advice).