Remote Car Starter Can Drain Car Battery Within a Week

Quote of the Day

If a free society cannot help the many who are poor, it cannot save the few who are rich.

- John F. Kennedy


Figure 1: 2016 Honda CR-V.

Figure 1: 2016 Honda CR-V.

My Montana-based son mentioned that his wife's 2016 Honda CR-V (Figure 1) will not turn-over after sitting in the garage for five days. To be honest, there was a part of me that wasn't surprised in the slightest that the car wouldn't start. What do you expect to happen when it has been at a standstill for five days? The other side of me, though, thought that something more serious had to have been going on if something like this had happened in such a short amount of time. I'm just thankful that it was this problem we had to deal with and not something more severe. Imagine if she had found herself in a car accident because of underlying problems? It would be unthinkable, but I guess we should be lucky that my son's wife had taken the time to read something like this safeco insurance review when it came to renewing her insurance policy, so at least she would be covered if something else were to happen. Of course, the fact that it wouldn't turn-over is worrying in itself.

No starting problems had occurred prior to early November. Unfortunately, I have had my share of car electrical problems and some of these problems have been hard to find. However, this is a new car and under warranty, so I recommended that he just take it into the dealer. He took the car into the Honda dealer, who told him that this is the result of the current discharge imposed on his car battery by his aftermarket remote start system (with cell phone interface, sometimes called a drone), which was verified to be within specification –the car was operating normally.

In this post, I will discuss why this behavior is normal considering how the remote starter works and recent weather changes in Montana. I should mention that all modern cars will discharge their batteries over time because their computer systems are always on – their nominal current drain is about 30 mA. Even without a remote starter, the cars will discharge their batteries after about 3 weeks (Appendix A).



Cold Cranking Amps (CCA)
Cold cranking amperes (CCA) is the amount of current a battery can provide at 0 F (−18 C). (Source)
Parasitic Current Drain (iP)
Parasitic current drain can be defined as any electrical device that draws electric current when the ignition key is turned off. In the case of a remote starter, the radio receiver must be powered so that it can receive the starter signal. This receiver current draw is parasitic current drain. (Source)
Ampere-Hour (Ah) Capacity
An ampere hour or amp hour is a unit of electric charge, having dimensions of electric current times time, equal to the charge transferred by a steady current of one ampere flowing for one hour, or 3600 coulombs. Battery charge capacity is usually rated in Ah. (Source)

Battery Capacity Versus Temperature

Figure 2 shows the impact of temperature on the capacity of a lead-acid traction battery.

Figure 2: Traction Battery Capacity Versus Temperature.

Figure 2: Traction Battery Capacity Versus Temperature.

CCA Versus Battery Capacity

Figure 3 shows that a battery's available Cold Cranking Amperage (CCA) decreases with reduced battery capacity. For the analysis of this post, I will assume that a battery's available CCA reduces proportionately with its capacity. Figure 3 originally came from a Yuasa technical specification.

Figure M: Battery CCA Versus Capacity. (Source)

Figure 3: Battery CCA Versus Capacity. (Source)

Cranking Current Required By a Car Versus Temperature

Figure 4 shows that the battery's available CCA decreases with lower temperature as the car's need for cranking amperage increases. I refer to this situation as "bad squared".

Figure 4: Car Cranking Amperage Required Versus Temperature. (Source)

Figure 4: Required Car Cranking Amperage Versus Temperature. (Continental Battery)

Problem Statement

Here is what I was able to find out about my son's situation:

  • His remote starter is rated to have a maximum parasitic current draw of 75 mA.
  • The measured remote starter parasitic current drain is 70 mA – it is within specification for remote starter units with a cell-phone interface. Other folks report similar parasitic loads.
  • Separate from the cell phone-based car starter parasitic current drain, the car itself has a parasitic current drain of 30 mA to support its onboard computer. This means that the total expected parasitic drain is ~100 mA = 70 mA + 30 mA, which is in rough agreement with reports on other web sites.
  • The car battery experiences the parasitic current drain for 5 days.
  • His wife just had a baby and is on maternity leave. The car had been driven every day prior to October 30th. After October 30th, the car has been driven sporadically.
  • The car is only driven short distances. I am guessing that the battery is never fully charge because of how it is started, driven a short distance and stopped. I will assume the battery routinely sits at 75% charge during normal use. In fact, cars brought in for service typically have batteries with 70% of a full charge.
  • The weather recently turned cold. The temperature had been in the 70 F (~25 C) range and now is about 18 F (-8 C) in the morning when the car is being started. This temperature drop reduces the battery capacity to 60% of its charge at the specification temperature (77 F).
  • I will assume that the effective CCA rating is proportional to the Ah rating, which is illustrated in Figure 3.
  • The car battery is rated for 500 CCA. I do not have a specification for its ampere-hour capacity, which is important when determining capacity. Batteries of similar size and CCA ratings have a capacity rating of 50 Ah.

This is enough information for me to figure out what is going on.


Figure 5 shows my analysis of the battery capacity. What I calculated is that the battery's capacity has reduced by ~75%. This results in a large decrease in the cranking amps available (justification in a later post) and results in slow or no cranking when attempting to start the car.

Figure 5: Battery Capacity Analysis

Figure 5: Battery Capacity Analysis


I am afraid that an additional parasitic battery load of 70 mA is enough to drain the battery sufficiently after five days to make starting difficult or impossible. This reminds me of a battery problem I had in my youth where a glove compartment light did not turn off and would slowly drain my battery. I could fix the light problem, but the remote starter must draw current to detect the radio start signal.

Appendix A: Computer Parasitic Leakage Example

Figure 6 shows a manual excerpt that illustrates how modern cars have computers that constantly drain charge from their batteries.

Figure 6: Chrysler 200 Manual Calling Out Battery Discharge.

Figure 6: Chrysler 200 Manual Calling Out Battery Discharge.

This entry was posted in Batteries. Bookmark the permalink.

25 Responses to Remote Car Starter Can Drain Car Battery Within a Week

  1. mark tucker says:

    Wow - 70 mA is awful for an always-on receiver. That's a pretty stupid design. Surprised these things don't use Bluetooth Low Energy (BLE) by now. Average currents would be in the microamp range. The operating range associated with the 2.4 GHz frequency probably wouldn't be as good as the 900 MHz (or thereabouts) product mentioned above but not by a huge amount. The BLE option would probably draw less than the self-discharge rate of the Lead-Acid battery. Certainly somebody somewhere must make something with better than 70 mA of continuous current.

    • mathscinotes says:

      I thought 70 mA was awful, too. I checked their specification and their max idle current was 75 mA.


  2. Filip De Somer says:

    Out of curiosity, how much would a board computer use in a non running car?

    • mathscinotes says:

      Hi Filip,

      New cars with on-board computers have 25 mA to 35 mA of parasitic current drain (Reference, Reference). So these vehicles will discharge their batteries after 2 to 3 weeks of idle time.

      The parasitic current drain is time-dependent. For example, some vehicles draw almost 1 A for a short period of time (~20 minutes) after being turned off (Reference). I have no idea what all this current is doing, but I have seen a number of reports discussing large current drains immediately after turning off the car.

      My old Ford Econoline van (i.e. no computer) draws less than a milliamp when idle. I have left it sit for over a month and it starts fine every time.


  3. Filip De Somer says:

    Mark, thank you for this information. Best regards, Filip

  4. Pingback: Battery Freezing Math | Math Encounters Blog

  5. Good job says:

    Good post, keep

  6. Lookingup says:

    Excellent post! I had the same issue recently, now that winter has started. Although my remote start system doesn't have a cell phone interface, it drained my battery within a week and a half, over the Thanksgiving break. I suspect that my battery didn't get a chance to recharge fully recently, since I hadn't driven the car much. Keep posting.

  7. Kathleen Alagna says:

    I live in NYS & the temps have been in the single digits during the day & @ 10 below zero at night for weeks. My car is parked outside & on days that I don’t use it, I’ve been starting it with my remote starter, letting it run for @ 10 minutes, & then turning it off remotely. The car has started without any issues. The last time I drove the car was on 12/30. When I started the car remotely on 12/31, it took 3 attempts before it started. At that point, I realized that I needed to start the car more than 1x/day & started it every 12 hours. It started right away last night but when I tried starting it this morning (@12 hrs later), the battery was dead!! Note: the car was sitting for a full week without being driven prior to 12/30. Is it possible starting it remotely drained the battery? How do I prevent this from happening in the future?

    • Doug says:

      When you start the car it puts a huge drain on the battery to turn over the starter motor. Idling for a few minutes will not charge the battery back up in any significant way - it need to be driven, preferably for over half an hour. (Idling the car for that long isn't good either). So starting it and not driving it is a bigger drain than just leaving it. Best would be to hook it up to a battery charger if you can/don't need to drive it. There are some battery maintainers that run on solar power, that could be left in the windshield if you have no way to plug in.

  8. Kathleen Alagna says:

    As an added note to my last comment, I don’t understand why I had no issues starting the car daily with the remote starter during the week that the car was not driven, but then had an issue with starting the car the day after the car was driven.... I’d appreciate any & all comments!!

    • CharlieL says:

      Hi Kathleen, how long was your drive? Was the drive at night? Headlights, other running lights and accessories (like heater fan) would be a significant drain the battery, perhaps negating any charging from the drive. Also each time you start the car (or it cranks and does not start) it drains the battery a bit more. If just leaving the car at idle (on days you start it) for 10 minutes I'm not sure how much the alternator charges the battery at low engine RPM (idle). I believe most alternators charge better at 1500 rpm or higher. (Don't hold rev at 1500-200 RPM until engine is warmed up). Also, with the very cold weather stretch we've been having in the northeast, the longer it sits and colder it gets, the less output the battery will have (as shown in graph above). I had issues with my battery (recently replaced, no improvement) if my car sits for 5+ days during winter. I believe it's because of my remote starter causing a parasitic drain. I finally purchased a "float" type battery charger for $20 and keep it connected to my battery when parked at home during the winter (for more than a few days). Also age and condition of the battery will obviously affect charging rate and how long the battery lasts. I find that after 3 years most batteries don't do great during cold weather. I hope that helps!

      • Andres says:

        So replacing the car battery did not solved the problem? I’m having the same issue

        • mathscinotes says:

          My son was living at high altitude where it goes below freezing every night. The battery lost so much charge that its freezing point became near that of water. The battery froze, split, and was destroyed. He replaced the battery and then made sure that the care was driven every few days to keep it charged. No lead-acid battery will survive an extended discharge at below freezing temperature.


  9. Kathleen Alagna says:

    Thanks for your detailed reply. I drove the car @2 miles. It was off for @3 hrs, started right up, then I drove it back - 2 miles. I always leave the seat warmers on, but don’t turn on the heat until the car is warmed up. When I start it remotely, the only draw on the battery besides the obvious, are the seat warmers & the running lights. When I drove the car, I turned the heat on along with both defrosters, the lights, & the radio. I also have an alarm on the car & a GPS.

    A friend gave me a jump start & said just starting the car without driving it more than a few miles won’t allow the battery to charge fully. I drove @ 10 miles after the jump start, turned the car off & the battery was dead again the next day. I contacted the company I purchased the car from & who does all of the maintenance. They informed me that my last battery purchase was in Jan, 2012, so I’m due. The temps where I live are expected to be @ minus 4 during the day & @ minus 15 at night this weekend with a wind chill of @ minus 30. I hope those temps don’t destroy the new battery!! I’ve never heard of a float charger. I’ll look into it. Thanks again for taking the time to supply so much info. It was very informative.

    • mathscinotes says:

      Hi Kathleen,

      Sorry to hear about your troubles. I want to mention a couple of things:

      • Starting a car in cold weather consumes quite a bit of the battery energy.

        The alternator does not charge the battery very quickly. Running the car for ten minutes will not provide enough charge to make up for the energy lost during starting. For more information, see this post. Because the alternator has relatively little spare capacity for battery charging, the high electrical load you have during driving is reducing the ability of the electrical system to charge the battery.

      • The battery state of charge is a complex function of usage profile, car charging characteristics, battery age, and environmental conditions.

        I work with batteries every day. A six-year-old lead acid battery in a mission critical application needs to be replaced. The failure characteristics of old batteries are unpredictable and it is better to just get a new battery.

      • A float charger is an inexpensive, low-current battery charger.

        I have five or six of them. They are all wall-warts that I use to charge my weed wacker and lawnmower batteries. The term float means that they hold that battery at its float voltage, which is the voltage at which the battery state-of-charge will stay constant (i.e. input current just balances internal losses). They do not charge a battery fast, but will bring a battery to full charge if left connected for a long-period of time (i.e. more than 24 hours).

      • If your battery is heavily discharged, jumping the car gets it started, but you really should put a charger on it to bring it to full charge. The alternator just takes too long (link).

      I know it sounds complicated, but the solution is simple: Buy a new battery, make sure it is fully charged when installed (new batteries often are NOT fully charged), and drive your car occasionally with some duration. Otherwise, put a charger on the battery when it is not in use.

      My son is going through this same sort of issue with his wife's car. She drives it every couple of weeks and the battery has discharged down to the point where it won't start for her. Since he has a new battery and it is cold (i.e. dramatically reduced capacity), I am telling him he needs to put a charger on it.


  10. Tina says:

    Hi can anyone help me I got a new car February 2016. I bought a Ford Fusion 2016, so a week later I called ford to find out about a remote start and they said they didn’t have any appoinment for 3 months. So I went and got one somewhere else. It’s a viper. Well I haven’t had no problems at all with it. Well theee months ago my battery stared draining so I took it in they said they didn’t find nothing wrong and that the remote start may be the problem and I was like I have had it for 2 years why now? Well they fully charged my battery and 3 months later it started again out of no where and now my battery smells like rotten eggs. I need some help please. Could it be the remote start?

    • mathscinotes says:

      A battery that smells like rotten eggs is a sign of sulfation – this is not good. Sulfation usually happens when a battery has been left in a discharged state. Do you drive your car often? Does it sit for long periods, like a week or more? Both my son and I have Honda CRVs (he actually has two). Like you, the dealer had long waiting times for remote start installations, so we went to private parties for the installation. I do not recall the remote start vendor. In my case, the car is driven every day and there has been no issue. Unfortunately, my son leaves his car in the garage for periods as long as 8 or 9 days and he has gone out to a dead battery. Eventually, his new battery was ruined. The mechanic measured the current draw on his remote and it was ~70 mA, which will drain the CRVs battery in about a week.

      There are many things that can stress your battery. One possibility is the parasitic load from the remote start. Other possibilities include poor electrical insulation, issues with the car's voltage regulator (maybe the battery is not charging fully?), or the battery may have gone bad (do you live in a hot climate? A friend in Phoenix changes his battery every year or two).

      Any mechanic can check the load on the battery from the remote start and the output voltage of your voltage regulator. I am afraid the best solution is to take your car into a mechanic that you trust.


  11. Cold van in Minnesota says:

    Hi there, thanks so much for sharing all this info. I’m curious if there’s any good solution for having a remote starter installed & preventing battery drainage...? We have a Remote start on my husbands car, which he doesn’t really use & he has always believed it drains the battery, due to repeated battery issues & new batteries the past 3 years. I drive a Toyota Sienna with our children (so I don’t really want to switch vehicles with him). Despite having battery issues with our other car, I would really like to install a remote starter on my Sienna if there is a way to prevent battery drainage. We live in a cold climate, our vehicles are parked outside, and we have a long distance to vehicles from our house. Also, we don’t have a garage or driveway so both dead batteries and frozen van doors are particularly challenging to deal with when I have 2 young children in tow.

    Do you know of any type of remote starter that you might recommend that is less likely to drain the battery? Or—if we install a typical remote starter, fully charge the battery, and get a float type of charger you describe, would this be sufficient to prevent battery drainage?

    Thanks for any help you can give!

  12. dodie says:

    Im on my 4th new battery I run my car daily I have to jump it at least 3 or 4 times a week I am sooooo frustrasted. But I just read to put my car starter in valet mode

  13. Omar says:

    Amazing article, thank you so much! I had a bunch of "mechanics" tell me that it was not possible for a remote starter to drain your battery over a week. I did all the testing myself and found a very similar parasitic drain to the one you found. In my case the on-board computer drains more than new cars, so it was contributing to the issue. I added a toggle switch for the remote starter system and I just turn it off when I will not drive for a while to avoid any battery issues.

    • Lenz says:

      Where did you get information on the toggle switch? How was it added? How long do you go without driving it and the battery is fine?

  14. Paul says:

    After three trips to my regular mechanic and two to the dealer (not to mention hundreds of dollars wasted on fixes that fix anything), the dealer finally got to the bottom of a year-long hunt for what was draining the battery in my 2013 Lexus (sometimes after just two days): the after-market remote starter that was on the car when I bought it. Removed it completely (didn't really need it) and problem gone.

    • mathscinotes says:

      Oh, the joys of the aftermarket remote start. Besides draining the battery, we have also traced a weird electrical system shutdown problem to our aftermarket remote starter. The funny thing is, our Honda dealer told us not to buy their remote starter because it was unreliable.

      We are in the process of removing our aftermarket remote starter completely. It is too much grief.


  15. Greg Bankston says:

    Well, my aftermarket remote worked without the battery not starting for 5 years and suddenly now it seems it might be the problem.

Comments are closed.