Bad battery or something else

[Bratman91]

I have an IS250 which is now 5 years old. About 9 months ago, I went to start it and there was almost no power whatsoever in the Battery. The AA got me going with a jump start and, the next day I took it to Lexus but they could find no fault. Since then, the car has worked flawlessly. However, two days ago, I found the Battery so flat that even the clock had stopped. Once again, the AA got me going and said that the Battery was probably bad as the voltage was low and the ampere-hour reading was about a third of what it should be. I had the Battery replaced at a specialist company and they also said that the Battery was bad. I do only about 5000 miles per year and the Battery specialist said that a very low mileage often resulted in batteries not being fully charged and this caused decay. However, I am concerned that, on both occasions (when no lights or accessories were left on), the Battery was discharged fully albeit after a few days. I am worried that a very intermittent fault might be causing a severe drain on the Battery. Any comments?

 

 

 

[scudney]

To be honest with you I don't think you have anything to worry about,I usually change my batteries on average every six years as by then they are past there best,the Battery 🔋 in my Lexus IS250 was checked last year and was okay and passed the drop test,however as I only did a thousand miles between last year and this,went to start it about 6 weeks ago and it was a bit sluggish and the next time wouldn't start,so I had to use a jump pack to start it.Took it down my garage and had them test it and it came up bad and replace,so had it replaced,hope this helps 😊 

[Herbie]

Original Battery 5 years old and only 5,000 miles a year. Some of those miles presumably in winter when you have headlights on early and for longer, heater, demister, deicer, heated rear window and maybe heated seats too. All that drain on the Battery with no real chance for the alternator to recharge it properly leads me to think the Battery has just given up the ghost and did indeed need to be replaced.

However, there are some tests you can do to prove the hypothesis but at the very least you'll need a multimeter.

First, check for what the 'standing voltage' of the Battery is and compare to this chart:

Next, fire up the engine and see what voltage is at the Battery terminals now that the alternator is spinning - it should be about 14.2V if the alternator is working. Now turn on the headlights, heater, heated seats/rear screen etc., and the voltage should still be above 13V. If everything is OK then you've just proved that the alternator is working well and is charging the Battery as it should. If the voltages are down then get your alternator checked by a proper auto-electrician rather than a 'traditional' mechanic.

Remember that there is a certain amount of current draw when the car is just parked up, such as the alarm system, the radio memory and presets etc., but even so, you should be able to leave it standing for weeks rather than days and it'll still fire up when you need it to. If the Battery is losing so much charge that it won't start the car then it's possible that you have a parasitic drain that needs investigating. If you want to do it yourself there are plenty of videos on Youtube showing you how to do it, otherwise it's our friend the auto-electrician again.

[Bratman91]

Many thanks scudney and Herbie. I feel a bit more comfortable after your comments and will check out the voltages as you suggest, Herbie.