12v Battery Is Discharging, Re-Charge Now !

Thanks, that confirms what I observed.

 

Excellent. That's also what I've though I was seeing in the past when my 12V was a bit low. No numbers to prove it until now. Your work is appreciated.

 

Nice work @Salamander_King !

So far I have left my Prime untouched for a week inside an insulated garage, I still get the Ready mode with no issue after a week.

Would it be ideal just to put the car into Ready mode once every few days for 5 mins (listening to the radio) without plugin at all so to keep a healthy 12V? Assuming we are still with covid-19 lockdown

 

Yeah, 5 min on READY mode is far better than plug-in for 3 hours. I just drove my car for a short 10 miles trip today, and the 12v SoC was up to 12.74v from 12.4v. But I think if the 12v is healthy, weekly drive is all it needs to keep it charged, although over time, the resting stage SoC tend to drop lower. Good full charge with a smart charger once in a while will probably rejuvenate this slow deterioration.

 

5 min of ready would be a nice before and after voltage test

 

I would do the 5 min READY test, but I just drove my PRIME for 10 miles short trip. 12v battery is now up to 12.7v. It will not get much higher than this. I will have to wait a few more days or deliberately drain the 12v battery to do the test.

 

Optima Yellow Top, 5 years young coming September. We're doing about 4000 miles a year, in good times. Yesterday I gassed up: 18 liters (4.5~ gallons), in over two months. It basically lives on a smart charger. Goodly drive yesterday, did a little hiking. Anyway, it sat overnight, hood popped, no charger, then first thing this morning (before reconnecting):

 

i'm wondering if the new non agm's have the same voltage characteristics

 

Should be somewhat lower. FWIW, that's the highest I've ever seen ours, maybe some amount of surface charge still.

 

Interesting replies. Thanks for all of the perspectives.

Currently, my vote is that something in the car's system downstream of the battery is sucking juice that it should not be consuming when the car is "off" The big pointer is the relay cycling that happens when the 12v battery is low.

The investigative suggestions are good, especially recording the amp and voltage when the car is not in use. Any suggestions on methods to do this... for example accessory battery voltage is available in obdc so that might be something such as Torque could write to a graph.

Will take a look but hope that others will offer some options as well.

Beverly Howard

 

Great minds think alike. For the past several decades, I have installed small polarized connectors on all of our cars ...plus my bikes, mower and now tractor with trickle chargers mounted overhead and cords easy to grab. As you know, doing that makes a huge difference in battery life.

However, I never expected that doing so would be necessary on the Prius since it has a high amperage charger attached to it every time it gets home.

Beverly

 

>> Curiously, what is your plan for 12v battery resurrection ? <<

It's a radical concept...

...tomorrow, I will be headed to an auto supply to purchase a new 12v battery.

The tests that I have done since that post indicate that the battery is not salvageable, notably by it's hydrometer readings...

...so, I also withdraw my previous assumptions.

My prior post was related to the apparent need to provide a constant trickle charge to the 12v battery to keep it from discharging completely.

A related question... any special tricks for disconnecting the positive terminal and moving it out of the way or does it push away easily?

Beverly Howard

 

Here is summary of my 2020 PRIME 12v SoC changes since 4/19 when I started monitoring the SoC using BlueTooth Battery Monitor II. The module is directly attached to the 12v terminal and read voltage every 2 min. The historical data is stored in the module up to 35 days, but I can keep the data indefinitely by synchronizing it to a smartphone app over BlueTooth. I sync only a few times a day to conserve the battery drain. The daily chart created by the app looks like this.


Daily historical data can be exported to excel. I complied all data from 4/19-5/11 and plot them on excel. I get this graph.


The problem is that with every 2min data point, the graph becomes very busy. And charging events (both external charger or by on-board charging system) bring the 12v voltage above 14v while charging, which makes very difficult to see the resting voltage changes. I plotted daily reading of voltage at 7:00am and also plotted voltage shortly after the charging events on the same day. I get this summary graph.


Some observations with 2020 PRIME LE, driven once a week (plus additional short drives in 3rd week).

• using external charger bring the 12v battery SoC higher (~13v) than using on-board internal charging system (12.7v-12.8v)
  
• max SoC by on-board internal charging system decreases slightly each week (12.81v, 12.79v, 12.76v)
  
• first 24-48 hours 12v battery drains most at ~0.1v/day and less drain/day subsequent days
  
• ~1.5hr once a week drive is sufficient to keep the 12v battery SoC to stabilize around 12.4v after 5 days
  
• short 10 miles drives is insufficient to bring the 12v battery SoC 100% (12.7v)
  
• ~3.5hr L1 charging had almost no effect in replenishing 12v battery SoC (from 12.38v to 12.42v)
  
• turning SKS OFF from the fob had no effect on the 12v battery drain

Next week, I plan to turn off the SKS in the car using Carista. I will report if that will have any effect on the first 24-48 hours of the 12v battery drains. I do not have Safety Connect service on my car, so there is no telematics draining the 12v battery. I don't know what else can be turned off that maybe using the 12v battery while car is parked. Any suggestion?

 

Good info, thanks!

 

I don't know what else can be turned off that maybe using the 12v battery while car is parked. Any suggestion?[/QUOTE]
2 things that I did that made a noticeable change are

• removed my OBDLink LX
• turned off charging schedule

Prior to doing the changes, I was seeing drawdowns > .10/day. Since the change, 2 weeks ago, I've been over .10 3 times and the median is .04 with several .02. I've only driven twice in the 2 weeks for a total distance of 10 Km.

 

Were you charging your car during that time? I guess, even without charging, having the schedule set up may "wake-up" the computer and check if the charge cord is connected and check the traction battery SoC level. Yeah, that's worth experimenting deleting the schedule settings. Thanks.