I'm curious about your wife's driving pattern. No I'm not a stalker. Is it mostly short trips?

All lead-acid car batteries sulfate quickly when not at full charge. If her daily drive is limited to a few miles, then expect a battery replacement in less than 2 years. The added drains (remote starter, allstate nanny) probably contribute to this state. A battery tender would help this, but the cost of this, and the hassle of installing with a plugin (and plugging it in all the time) is more effort than it's worth. Unless it's done daily, the battery is at partial charge and sulfating, which kills it.

Unfortunately, Honda chose to put small capacity batteries in this car so there's not much margin for failure, especially in a cold climate. If this latest fix doesn't hold, consider replacing the battery in the fall each year. NAPA sells a good battery, reasonably priced (under $100), in the correct size.

I'm not a fan of sandwiching larger batteries in there (requires some modifications) but this is an alternative that would give longer battery life.

 

Yes, It wouldn't hurt to disconnect the remote start.... just to rule it out...

But, yeah, short trips kill batteries.... and kill cars.....(more so, older vehicles) but, stilll a car needs to be run at Operating temps.....(help burn out the junk...)

In getting a new battery...... Do it..... and leave remote start disconnected for some time........ bring it into the picture down the road.....

After you are comfortable that is seems the new battery is behaving (as new batteries should)

 

 

I'd be chasing wires like crazy, listening to the alternator pulley.. that remote starter would have to tap into an 'always hot' circuit, have a little relay and go to the ignition wire, no? I'm no electrician and hardly a mechanic.. but I'd check under the fuses in the engine bay just to see whats up.. i wonder if a crappy connection or relay could allow power from the battery to bypass the ignition, giving power to junk in the cab. Maybe consider, with the car off, popping out relays and jumpering with that multimeter of yours to see whats live, maybe mark the hot relays with a bit of tape. could give you or your mechanic a starting point. Itd have to be an always hot circuit if the battery and the alt are both perf, wouldnt it?

it sounds like you're good to go already, but maybe this'll get the gears turning for someone else.

 

There should always be some drain on the battery. Various systems stay awake to operate remote entry, maintain radio presets (and anti-theft), and retain volatile memory in other control units. This is called a "parasitic" load.

The Fit service manual specifies this load to be 200 milliamps (mA) or 0.2 amps when all the systems are "awake." Most go to sleep after about 40 seconds of inactivity (i.e. no door opened) and the load drops to 35 mA (0.035 amps). Disconnecting the battery negative cable and putting a multimeter in between this cable end and the battery should give you an accurate mA reading. Be careful not to overload the multimeter as these typically only handle a few amps maximum. Trying to start the car in this mode will burn out its fuse. There are more clever ways of doing this that involve more expensive test equipment.

If something is sending a sporadic signal to any of the car's control units, these will remain awake and draw at the higher amount (10 times higher) than when asleep. I'd be concerned this is happening with the aftermarket devices (remote starter, insurance nanny). Or the devices themselves may have a high load (the remote starter has to keep a radio receiver powered up to listen for start requests).

Your mechanic may be using a load monitor typical for checking starter load which measures in the 100s of amps and not registering the parasitic loads.

I read once (may have been here) that car designers allow for 3 or 4 weeks parked in sub-freezing temperatures and still have enough battery reserve to start the car. Hondas are no different, but have less of a margin due to the tiny batteries.

151r batteries are about 45 amp-hours in capacity. A 0.2 amp draw (200mA) will drain it in 225 hours (9 days). 0.035 amp draw (35mA) is 1,286 hours (53 days). Not sure how much remaining capacity is needed to actually start the car. This depends on the ambient temperature and other factors but you can see how a 200mA (0.2 amps) will deplete the battery in about a week. This is when the battery is new. As it ages it has less capacity due to sulfating which occurs more rapidly when the battery isn't maintained at full charge.

 

I’m surprised nobody has mentioned the ELD equals electronic load detector or some auto places call it The battery current sensor.

in any event there’s a TSB on certain Honda models to replace the ELD due to faulty soldering. But as with other TSB’s I’m pretty sure it Should have extended to other models with possibly different part numbers but that are similar and that are not listed on the tsb.

On the Honda Fit it doesn’t seem extremely common but with high mileage fits somewhat common for the ELD to go bad and this could cause battery issues Such as not recharging properly or parasitic drain.

Lastly I just wanna say that despite the Honda Fit having one of the smallest weakest batteries as a stock battery it should not die overnight or even after a couple days of sitting that means you likely have a parasitic battery drain or problem recharching Not related to the alternator if the battery and alternator tests good and it could be the ELD (or battery current sensor).

 

I've been thinking about this statement. The Honda OEM battery is not just small and weak; it is inferior in quality. I've been getting more confident starts from my Interstate 151R. The Interstate 151R is also better than the Duralast Gold 151R.

 

This thread is from 2018…… also the OEM battery is more the adequate, I live in Canada and I have had an oem Honda battery in my car for 5 years with no issue. The big issue here is not the size of the battery it’s not buying a factory Honda Battery (which are no more expensive than aftermarket but way higher quality).