12V battery study

wow! i check mine once a month or so. i open the hood the night before and check the jump point in the morning. it's been 12.7 since i started checking in april 2015. it's 42 months old.

 

I find after sitting overnight, the battery will be at some point, say 12.8. If the car isn't driven over the next few days the voltage will slipslide a bit more, say down to 12.6.

 

What exactly is the goal of the study? If I understand the procedure, you're simply measuring normal recharging current at two times shortly after awakening the car. The much higher currents after the door was left open are to be expected, although it's surprising that the voltage wasn't lower that time. Battery drain with any door (including hatch) open is about 0.7A, plus current to power whatever light bulbs are on.

 

+1 on the door... If you really want an unloaded voltage measurement, you should measure under the hood so you can do it with no doors open. For added accuracy, pop the hood when you're done driving, or at least do it from the passenger's side (so you don't open the driver's door and start the brake pump) and then wait a minute or three to let the battery recover. But as long as you're consistent in how you measure the voltage, it at least tells you something.

What are you using to measure the current? Do you have a clamp on one of the battery cables?

 

The other thing wrong is the "starting current" is actually a 50Amp pulse, about 0.5 second long.

Your readings indicate your 12V battery is in good shape.

 

because there is so little required of the battery, i believe a simple resting voltage is all that's needed. eleven years of experience hasn't proved me wrong, but i have never had to deal with a battery that measured in the mid to high 12's, but wouldn't power up the car.

 

It's very difficult to catch a mythical creature. Even if in mediocre condition, the 12-V battery won't absorb enough energy to affect fuel consumption noticeably, at least not directly.

The recharging currents you're measuring are in the opposite direction from the brief 50A or so discharge that boots up the hybrid system.

Another easy way measure battery voltage without the door-open drain is to fool the switch for the hatch by manually pushing the latch into its fully closed position (two clicks) while the hatch is actually open, then measure at the battery.

Good question about the voltage change. Temperature reported by the sensor near the battery is probably one factor in that decision.

 

if i forget to pop the hood the night before, i reach over through the passenger door.

 

The easiest method to monitor energy use is to buy a $10 ELM237 Bluetooth device and then run Torque on an Android phone to see the traction battery output current.

With my PiP in park, but in the Ready state, I typically see 1.1 amps. Turning on the headlights increases this to around 1.6 amps, but it fluctuates. What is the resting voltage of the NiMH traction battery? (found out it's 202 volts) Is it the same as the Li-Ion traction battery (found out it's 346 volts)?

Once my 12v battery gives out, I'll replace it with LiFePO4 to marginally improve efficiency and weight, and hopefully significantly improve longevity. It might even be cheaper compared to what Toyota wants for their OEM battery.

 

You could have it load tested at a dealer or any shop, battery retailer etc. with the right equipment, just a thought.

 

The prius 12v system doesn't demand much current to operate, thus it doesn't need a big. Battery!I had a 2014 subaru xv crosstrek hybrid. It had 2 12v battery 1 for the 12v system and 1 for the stop start system, the stop start was recharged by the hybrid battery inverter , every morning the hybrid battery was or almost depleted, the cycles that battery go thu I bet you that won't last for 3 years! I expect the prius battery should last me 5-8 years! I am thinking about replacing the prius battery w a agm battery cause I replaced the subaru 2 batteries w agm batteries,

 

And I noticed headlights was brighter, faster engine restarts, maybe slight mpg increase? And never had a depleted hybrid battery from the inverter re- charging the stop start battery .