Nearly drained battery for 2 weeks - how much damage was done?

Question

I recently made a mistake of starting my car, and only driving it for a short trip multiple times in below-freezing weather without letting the car fully warm up. This was after the car had sat for multiple weeks, so it drained the battery to the point where it could crank but not start in the cold. I made two attempts, but no dice. 2 weeks go by as I figure out what to do, then I used a battery jumper and it fired right up.

After that first start I took it for a good 30 min drive, after which it fired right back up, and has had no trouble since, but I'm afraid I may have done some damage by letting it get so low and not dealing with it for 2 weeks while it wasn't able to start.

The battery is at least 5 years old (that's when I purchased the car used), perhaps much older or even original (2010), but this was the first hiccup. Is it just time to replace it? Did I do some lasting damage, or am I overthinking it?

Answer 1

Considering car batteries usually have a lifespan of between 3-5 years, I'd say "yes" you should probably think about getting a new battery.

As far as damage to the battery, you should have no doubt in your mind some damage was caused. As far as how much damage happened, there's really no way to tell exactly. What happens when it becomes drained like that is the plates start sulfating, which means the sulfur in the sulfuric acid starts depositing itself onto the plates. Over time this causes the battery to not work as well. You'd only notice that the battery may not spin the engine over as quickly, or you may not notice anything until the battery just decides it's not going to work any more. However a battery dies, it usually dies when you can least afford it to happen, whether monetarily or time wise ... it just seems Murphy will raise his head at the least opportune time.

Bottom line, it is my suggestion to replace the battery as it has lived a long and full life. Time for a new one to take the reigns and become one with your vehicle.

Answer 2

TL;DR

Keep using it till you can no longer use it if you're not afraid of getting stranded somewhere; it's a $150-$250 investment depending on your engine size.

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A 5 year old car battery has lived a good life. Regardless of your recent actions it's likely time to start thinking about getting a new one.

The battery in my 2011 Honda Accord needed replacement during nice fall weather in 2017; Central New York. It simply failed to start up in the morning before work so I jumped it using my wife's car and then spent the work day worrying whether I'd be stuck at the office, hah.

A few days later I experienced another failed start so after work I picked up a new battery with about 100 more cold cranking amps (CCA) than my current battery and the difference it made was like night and day. I never realized how I got used to slower and slower startups as the years progressed. Heh, it's about time I start thinking about a new battery again.

The battery in my wife's car decided to die at almost exactly 5 years old when trying to come home from the store with our two toddlers. She was stranded in the parking lot until I could come and jump start her. This was obviously unacceptable with two toddlers so I bought a new battery on the way home.

You could also consider going to an auto parts store or auto shop and ask them to test your battery for you. They should be able to quickly tell you if you've killed a cell or if the battery cannot maintain voltage under cranking load.

This is an awesome video if you're looking to test it yourself: https://www.youtube.com/watch?v=YC--MLNIbik

Answer 3

You never had a charging problem. The charging system worked as intended.

The lead-acid battery has simply reached that age, and is due for replacement. It doesn't owe you anything.

Yes, you did damage the battery with both actions of a) draining it below 70% full, and b) leaving it in a discharged state for any length of time. These are both things to NOT do to a lead-acid battery. Yes, these (and others) are appallingly shameful characteristics for any battery. The reason we put up with it is cost. 30-year batteries resilient to abuse can be had, but cost more like $1000.

However, winter is the worst time for a battery. So if you made it through winter, you might make it through summer.

I would not count on another winter.

Answer 4

I did a recent capacity measurement (full charge/discharge/charge) after I left the dashcam + rear camera + navigation to completely drain my camper battery down to ~5V out of 24V.

The battery is 100Ah so calculations to percents are easy.

3 weeks prior the battery was 96Ah.

After being completely drained and recharged: 88Ah

i.e. honest 8% of the capacity are lost because someone didn't care to either double check that everything is turned off, to install the long-waiting in the basement solar panel or to install some overdischarge protection.

The battery is an almost new AGM with expected life of 500 charge-discharge cycles if the discharge ends at some sane voltage (e.g. 10.5V for a 12V battery).

The usual flooded starter batteries don't even have cycle life specified, but the practical experience shows some 30-50 cycles.

Wildly extrapolating, by allowing a starter battery to completely drain, you lose ~20% or ~50% of what is left and not much is left after good 5+ years of service in the first place.

Get a new battery and send the old one for recycling with the due honors.