Battery won't stay charged after replacing ignition coils
 

My 2007 Honda Fit Sport (~96k miles) was misfiring, so I replaced the ignition coils with some cheap ones off ebay and all seemed okay. After making the change the car started up just fine and the stuttering at stop lights disappeared! I thought all was perfect.

The next day my battery was dead. I jumped the car, let the car run for 30 minutes to charge the battery, and then tried to restart the car. It would not quite start - as if the battery had not charged enough. However, I was worried it could have been the fault of the ignition coils, so I swapped back to the original coils. Jumped/charged the car for 30 minutes. Turned off the car, tried to restart and it turned on with no problem. I thought for sure it was something with the cheap ignition coils and problem was solved. The next day, my battery was dead again! I tried the whole process again with a third (new) set of ignition coils (higher priced) and still the battery drains. I no longer think it is the fault of the ignition coils.

Did I somehow do something wrong installing ignition coils that is affecting the battery? I checked all my connections, the spark plugs are relatively new, the battery is only 6 months old, and I have no idea what I could have knocked loose or done to cause the battery to drain. Perhaps it's all just a horrible coincidence that my alternator started failing exactly when I changed my ignition coils, but that seems hard to believe. I am able to charge the battery, but it then just starts draining as soon as I turn off the car.

I greatly appreciate any advice or help figuring out what I could have done. Thank you!

It's a relatively new battery but that doesn't mean it didn't go bad---stop in wherever you bought the battery to have it checked. Shouldn't cost a thing and they can tell you if it is good or bad, even though it should be good. A cheap fix if it is the battery.

You were right!

I never even considered that a 7 month old battery could be bad, but the idea that it stopped holding a charge exactly when I replace the ignition coils just seemed too coincidental to be true. Tested the battery and it would not hold a charge. Swapped out the battery and all is good. Lesson learned.

I am wondering if somehow I killed the battery during the ignition coil change, but I have no idea why that would have been the case.

Dear eranro. Greetings. To make sure that the car's electrical system is free of current leaks, when turning off the engine and all current consuming equipment, disconnect the positive or negative terminal of the battery and connect in series a Milliammeter to measure the current that is drained from the batery. Do not start the engine. The current should be very low, around 40 mA or less.
To test the alternator, with the engine running, accelerate the engine a little (around 2500RPM) and activate several current consumers such as headlights and air conditioning and measure the voltage at the battery terminals. The voltage should be around 14 Volts. If the system passes these two tests, your car has no electrical problems and if the battery is discharging, is because it is defective, not the car. God bless you.

Dear eranro. Did you buy a cheap battery or have bad luck with buying a good brand? Here in Brazil there are good battery brands, like "Heliar" but there are also cheap brands (a little cheaper) that last for about 1 year. I don't know the quality of batteries sold in the USA. I think it must be similar to what is sold here. God bless you.

Interesting. Short of throwing it in a tub, I'm not sure how you could have ruined it. It could have just been a dud. Assuming the new battery hasn't repeated this issue, it's likely safe to assume the electrical system is still good.