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did Honda sacrifice my civic battery to juice their mpg?


Topic starter

For a 2018 civic hatchback (manual, base model), I wonder what my options are, since I would rather buy slightly more gas than replace expired batteries more often:  My battery died at just over 20k (but out of warranty due to the year).  The factory battery was a no-name made in Turkey.  The dealer parts counter man said he'd never seen one like it.  When I put in a replacement, and checked for good charging, I suddenly saw it not charging! (Batteries that are chronically under charged are known to die young.)

After much measuring and searching, I found that Honda has used "dual-mode" charging in these for several decades as a way to juice their mileage numbers.  One of the car's computers continuously tells the alternator what voltage to generate, and it will vary between charging and not charging.  Sometimes, I've actually seen the voltage rise by 0.30 volts when the engine is turned off (measured at the accessory jack).  Honda apparently changed one aspect a few years ago, keeping a full charge going while the headlights are on, seemingly to stop customer complaints about headlights flickering.  One consistent behavior while the voltage is at some low level is that it is suddenly kicked to full when you let off the gas and are coasting or stopping.

This is obviously embedded into Honda's software, but I wonder if there are any tuning or configuration options to moderate battery stress in the name of mileage, such as not doing it unless the eco mode is on.

By the way, I watched Scotty's video "I finally got a new civic" and was surprised at his choice.  I had avoided the sport model, which asked for high-test gas, and had shorter sidewalls separating rims from potholes.  All I had really wanted was its fog-lights.  I also saved $800 by avoiding the scary CVT.  And I agree a plain handbrake is better, but I've had that break too.  (Even so, you wouldn't be pulling it as hard for emergency stopping as you normally do to lock the wheels for parking.)

2 Answers

Yeah of course you hit the nail and I had they make him to get better gas mileage but then the battery is going to wear out faster and then when the alternator system does break down it cost a fortune to repair


There's no point raising the voltage if the battery is already full and there's low load on the electrical system.

Overcharging will kill a battery prematurely too.


Multi-stage charging is pretty common these days, and it's working well for me. 5 years and counting on my battery and it's still going very strong. (good name brand).


suddenly kicked to full when you let off the gas and are coasting or stopping.

This could be a crude form of "regenerative braking". Should save you wear on brake pads.