Here's a new one.

Filled the car (2018 Sport Hybrid) and the mileage for that tank was excessively low....22-23MPG! We'd had some really cold weather, but in the past in cold like that it never got that low....usually 25-26 at worst. So, a few days after I refilled a second time, the battery died with no other warning signs. Analysis of the failed battery showed "failed storage capacity". Kinda surprised it lasted two years,

Got the battery replaced under warranty, but I do wonder of that excessively low mileage had something to do with that failing battery....or was at least a warning?

 

It is possible once it got close to the end, it simply did not meet the minimum capacity threshold.

 

My MDX Sport Hybrid mpgs will dip down to the 21-22 range the colder it gets. I figured it is because of only using the 3.0L hauling +4500lbs and having limited to no EV mode because of the electrical/heat needs. Still have OEM tires on the RLX and we try to limit near/below freezing driving.

Being an old fart, there use to be a saying of: "batteries die in summer; but, you don't find out until winter". Less of an issue today with sealed and AGM batteries that don't need to checked/serviced. My 18 RLX Sport Hybrid battery also failed back in 2021, with 15,000 miles, and replaced under warranty. It was during lockdown and only fueled the RLX once a month. I didn't pay attention to mpgs before/after the replacement. I had "U0104-00 ACC may not work properly with braking system" and "U1100 Gauge control module loss of communication". The new battery fix for both of our RLXs with different issues shows how complex and sensitive the hybrid system can be.

I had my OEM batteries fail between 3-4 years with my 3 previous and my RLX. Only my 19 MDX Sport Hybrid made it past the +4 year mark without issue (5 years in Mar/24). The only differences between all 5 Acura's is my 19 MDX engine bay isolates and insulates the battery, sits further away from engine, and has more natural air cooling. The RLX battery is more exposed in the engine bay, sits around 6 inches from engine, and has two radiator coolant hose almost touching the battery box.

 

The battery on the wife's '18 RLX SH died in the garage a couple of years ago. Fortunately I was able to charge it enough to start and then drove to get it replaced. No real warnings except that, during covid, I'd get warnings (email) from AcuraLink saying the level was too low to report info to the app. The car would start fine, and after starting the AcuraLink would say it was good again. That was the pre-warning to the failure of the battery - but it literally worked the day before and died the next. It was factory battery after 3 years but only 9k miles. Replaced under warranty - been good so far(knock on wood) even with car sitting for a week at a time...

 

been noticing my mpg slowly going down with the cold, too. I learned last year not to turn the heat all the way to max cuz that completely shuts off the hybrid system and my mileage TANKED. and no matter how gently im pushing it and trying to be in hybrid mode the mpg does not climb up. its gone down 2 whole mpg since the start of the cold (approx 3 months now). im currently showing 24.3. used to be 26.4.

 

Don't forget about the winter blend of gas, which will likely affect your spending at the pump - aka, you will have less MPG during winter/colder months...

 

Might be a good idea to get a battery trickle charger. Both my wife and I WFH so we drive very little. Those trickle charges helps. Already replaced the 12V on '17 MDX twice and '20 RLX once. All done under warranty thank goodness. That's what happens why you don't drive much.

 

+1 on Battery tender. Extended my previous car's battery life span to 7 years before replacement was needed

 

never heard of this. What does it do exactly?

 

It just a battery charger. It has two alligator clips that goes to your 12V battery, other end plugs in outlet. It help slowly charge the 12V while it's sitting idle for a long period of time. Prevent battery drains. My SA warned against using it, but I've used on both MDX and RLX without any issues.

Just search Amazon for: "battery tender plus 12v battery charger and maintainer". Costco also sells a nicer one.