[Tony martin]

Battery dies overnight when the rear window defroster is left on? How do I fix this issue?

 

[highvoltage]

The defroster is not on when the car is off. Your battery died for other reasons.

 

[emeron]

Don't mean to sound apathetic or snide, but the only fix (other than hooking up the battery to a tender) is to not leave the defrsoter on.

You can pick 2 out of these 3 from a car battery:

• Can feed the defroster all night.
• Can crank the engine in the morning.
• Fits under the hood.

 

[03LXV6]

Are you leaving the car on at night? The rear defroster works only when the car is on.

 

[2-DoorAccord]

The above replies are correct.
I'll add my 13 Accord 4-cyl. Will not supply enough voltage when headlights are off to properly charge my (last) AGM battery. Shame on Honda.

 

[Keyboard]

As others have said, the defroster doesn't remain on when the car is turned off. Something else is draining your battery.

It's more likely that you accidentally left something else on such as lights. For example, my sister kept having dead battery problems, and it turned out to be the ceiling lights that she kept leaving in the ON position, instead of the "Door Activated" or OFF position.

 

[Ronch]

@Tony martin - you left out some key info:

1. How old is this battery?
2. Do you park outside in the cold?
3. When was last time you checked the water level in each battery cell?
4. Etc.

 

[DonutLimo]

Sticky defogger 40A relay? Do you know how to test it?

Under hood fuse box, over left wheel well:

 

[tracienewham]

The above replies are correct.
I'll add my 13 Accord 4-cyl. Will not supply enough voltage when headlights are off to properly charge my (last) AGM battery. Shame on Honda.

 

[KW2004Accord]

An AGM battery is supposed to discharge at a slower rate and recharge at a faster rate than a lead acid battery. I haven't a problem with my AGM battery in my 2017.

 

[Ronch]

@tracienewham - You're assuming the battery monitoring sensor (BMS) and alternator are working correctly, and your battery cable connections, including ground connection to the frame, are all clean and tight, etc...