hi All,

I found my vehicle 12V battery was low at 11.45V on the NX350h so I trickle charged it. Last reading was at 12.65V yesterday as if 11pm.

Today, I looked and it's down to 12.43V at 8am.

Is that normal to lose that amount over night?

I saw some other videos including the ones on youtube from LSFT but not sure if there's an issue on my vehicle.

 

Mine typically drops about 0.2V between that timeframe. Which it seems to be very similar on yours as well. That is what I have seen, but typically it drops a little and not a long, but around 6am, it seems to do something and drops a bit more during that timeframe.

 

Thanks for chiming in on it.

 

I have seen similar drops in the 12v battery voltage overnight in both of my two 450h+ models. This occurs despite keeping the fobs turned off (holding the lock button, while pressing the unlock button twice) or keeping the fobs in a Faraday box when not using either vehicle. There is still a lot of "communication" going on with these vehicles which appears to drag the resting voltage down. I have only had the RX450h+ battery croak one time. Since I have installed a battery monitor on each of them, I get reports on my cell phone on a continuing basis and know when to put them in READY mode for about 20 to 30 minutes to charge the 12v. It appears to work well and I have not had any issues since becoming a bit more proactive. I end up doing this about every three to four days if I do not drive the cars. If one or both are driven, it does not seem to be an issue.

 

Yeah the voltage drops and jumps all over the place from any little things you do whenever you press something, open something, or keep something turned on... it is just scary lol

 

Just measured mine for licks and giggles. 11.32V after a full 4 days in sleeping beauty mode. It has sat longer without issues and my battery actually has to crank.

But voltage itself really isn't the best measure of battery health or charge function. I think its normal for a battery to show a high voltage right after charging that isn't necessarily an indicator of state of charge or health without a proper load test. I've heard the term "surface charge" which I believe refers to a kind of heightened voltage level that is a residual effect of charging that can dissipate very quickly. Voltage can show on the higher side of things, but have little capacity and fail a load test. Voltage can show a bit on the low side but still have significant capacity to provide high current. A load test (or perhaps a smart charger test) is the best way of determining battery health. A current draw test (putting an amp meter between battery post and cable) is a better way of determining the amount of parasitic draw. I think most cars will draw 30 to 50 mA just sitting, 50 to 70 a bit on the high side and above that is likely to cause issues (provided something hasn't woken up, like the EVAP system test as example).

 

hmm.. I drove it a lot today and I just checked the voltage. It's 12.14 now.

How does the NX hybrids charge the battery? We don't have an alternator, right?

 

There is no alternator. It is charge via the DC to DC converter. The DC to DC Converter in Ready Mode will supply current to the 12V and charge it.

 

So what voltage is too low, I saw in your video, you had a voltage measurement tool. Where did you find that at? Thanks

 

It's in the video description: ANCEL BM200. Since the link is a referral link - don't want to post it here.

 

physics/electrical - load resistance or impedance causes voltage drop. V=I*R (less phase shift) unloaded battery, full voltage Just what are the forum "Electrical Engineers" trying to measure?


YMMV,
MisCow3

 

Thanks but I was wondering about voltage checker - motomaster

Great video btw.

Did you find that on Amazon?

 

Thanks but I have the OBD2 that measures the voltage in addition to the battery meter. I'm trying to find the root cause of the voltage drop.

I'm an EE so I know about Ohm's Law.

 

It's those pesky resistance bugs connected to the battery terminals that draw parasite voltage and current. ... and by the way most forum members are not BSEEs, much less understand Ohm's law. Even with Ohm's law it is nearly impossible to get correct measurements while a battery is still under load , with a load that varies without much rhyme or reason.

YMMV,
MidCow3

 

Yeah, I just don't want to be stuck at a parking lot when the vehicle doesn't start. So far, no real problems except the battery drain issue.