[williamsji]

How often and regularly do you drive the vehicle, and for how long on average? It's a big battery, and does not suffer spike discharges from a starter motor.. so it should take 4-5 weeks to deplete it sitting.. but even partially depleted batteries can begin to deteriorate quickly.. so hybrids, just like the ICE versions need some regular driving, without major gaps in times between drives.

Let me take Toyota/Lexus as an example for a moment to set some context about hybrids. Toyota says that hybrids need to be driven (not parked idling, but driven) at least 60 minutes per week, or the 12v running battery may not receive sufficient recharge to continue working properly over the expected 3-5 year life span Toyota expects. And if you think about what the 12v battery in a hybrid is doing... this advice makes complete sense.

 

[williamsji]

Good advice.

We drive an average of around 20 miles a day. This new battery is one month old. (Had same problem two times with old battery).

Wife drove it 50 miles from home yesterday, then parked it at a mall. Came out 4 hours later and new battery was dead. Completely. After AAA jump she drove 50 miles back on freeway without stopping and it was dead again this morning. I charged it for 4 hours this morning and took it to dealer. They cannot identify any problems with battery or charging circuit.

I wonder if there is an intermittent loose short, connection or fuse somewhere.

Sorry, typo: new battery is two months old - not one.

Edited for clarity: both old and new battery deadness.

Well that is plenty of driving, so something else is at fault here.

I gather the dealer checked for abnormal parasitic drain, as well as confirmed that the 12v battery IS getting charged during driving, yes?

Since this issue is repeating across multiple batteries, if they have confirmed everything is working as intended.. then the next suspect is something being left on after the vehicle is parked, or an intermittent. Modern Hondas are fairly good at interdicting these sorts of things, but I doubt they cover every possible cause.

Personally, I would plug one of these into a 12v accessory socket in the center console and check and insure that the charging system (which is a DC-2-DC converter powered off the HV battery in the hybrids I believe) is actually working. I would expect that with the vehicle turned on you should see a charging voltage well above 13.5 vdc on the 12v power bus, until the battery is fully charged. If not.. then that is a problem as it indicates the battery is not being topped up while driving, and perhaps even being drained during driving. Your symptoms certainly would suggest a closer look into this aspect. [These little meters are common on Amazon, and they also provide you additional charging ports for USB devices. You can even get them with USB-C ports on them now on some brands sold].

 

[williamsji]

Thnx for your quick reply. Yes, dealer tech said they checked for drains, and adequate charging voltage. The tests they conducted seemed extensive.

I suppose I need to get one of those meters. Like intermittent electrical problems everywhere they rarely show up when at the shop. Doh.

I looked on Amazon. Plenty of meter options. Do you know if there is a model that comes with memory? I didn’t see one. Would like to let it monitor voltage for, say, 24 hrs then download the data. The 12v socket is way down in the center cubby. Impossible to see while driving. Driving safely, that is.

Also, I like plots and graphs, TBH.

If you want to log your 12v power bus (a good idea in your case I think), this is the item I personally use.

It will store up to 30 days of data (measures on one minute intervals) and you can read it and upload data to any smartphone. Gives you a nice graphical plot of data over time (which is great for checking on intermittent drains, as they will pull the voltage down some amount and be easily spotted). Example: when the automated purge cycle on the fuel system initiates conditionally about 5 hours after parking and shutting down I can clearly see it on my battery monitor as it draws several amps for about 15 minutes

You can also set this monitor to alert you by smart phone when voltage drops below a set level (which you can set yourself, or use their defaults).

Just be sure to actually close the app when you are not checking the monitor, to minimize any power drain from the monitor (only draws 1ma when in monitor mode, but will draw more current when it is active with the phones app). note: in my experience, the voltage readings can be off a bit, so just learn what the offset is and mentally compensate for it (mine generally reads about 50 mv low compared to an actual voltmeter reading, so I just compensate for that on my end).