12v Battery 'Life'

[Diver Fred]

Honda Jazz Hybrid; 21months old. Car has been garaged for 17days. Went to it this morning and the car doors would not open on the key fob. Unlocked car with key - no interior lights, Start 'button' does not illuminate and worst of all cannot get the gar out of 'Park'!

Can get to battery under the bonnet so can charge it up.

But am I wrong in expecting the car battery to hold enough charge to operate the electronics and start the car for more than 17days on a battery that is only that old?

 

[Mottie]

Have you accidentally left the lights/interior light/glove box light on? See if anything lights up when you connect jump leads to the battery or refit the battery after a good charge.

 

[carmanmemoranda]

Honda Jazz Hybrid; 21months old. Car has been garaged for 17days. Went to it this morning and the car doors would not open on the key fob. Unlocked car with key - no interior lights, Start 'button' does not illuminate and worst of all cannot get the gar out of 'Park'!

Can get to battery under the bonnet so can charge it up.

But am I wrong in expecting the car battery to hold enough charge to operate the electronics and start the car for more than 17days on a battery that is only that old?

Yes battery should last that long, as long as no additional drain is present

 

[Jurassicspark]

You can calculate it. Get the AH of the battery and measure the load when the car is asleep. Then you can go from there. However, a new good quality battery should keep it's charge for at least a month.

My battery is six years old and the battery will only hold charge for 3 days but it's no problem for me as I drive it everyday.

 

[ericmark]

I have also gone to car, and found battery discharged, also a Jazz, but much older, likely 20 old, although battery only about a year old, how long had I left it, not sure, we have three cars, so not used that often, but the main problem is there is nothing to show how well charged the battery is when we leave the car.

So after charging with a smart charger I know I can start it in three weeks time if nothing left on, boot light is the worst, so easy for boot not to close fully and light stays on.

But a lead acid battery takes time to charge, the lithium battery 2 hours and fully charged, great, but the lead acid it depends how long it has been left discharged, with an extreme case, a VRLA battery from a stair lift was left discharged for 6 months and it took 2 weeks to recharge, will not go into the story now, but it can take up to 2 weeks to fully recharge a lead acid battery.

So we do a 2 mile run, once a week, is that enough to maintain the battery, or will it slowly over time have less and less charge? Since no longer have option to use hydrometer can't give an answer, but likely the battery gets lower and lower as the weeks go by, so the question is will a ½ charged battery last 17 days? Or will a fully charged battery last a month.

I put my car on charge around once every 4 months to ensure the battery is fully charged, I use a Lidi smart charger so can walk away and leave it on charge, but using an energy monitor I get and over time the high charge rate reduces and the low charge rate increases, and because I have done it many times, I can look on my PC and say to myself that battery is as charged as it's going to get.

This one was my kia battery, 18th Jan 21, it failed early this year, likely some 20 year old, the bottom you can see how most the charge went in quickly, but 6 the following day before it dropped to a low rate, and top one shows the pulses it was getting to maintain it so 12 hours latter, does not matter how big the charger, the battery can't absorb charge quickly it takes time.

 

[norseman]

Preaching to the converted no doubt but battery life is so unpredictable these days due to cars being stuffed with equipment that likes draining the power. Batteries in older cars last far longer in my extensive experience with their ownership .. my late 'eighties Classic will stand outside for up to four weeks (maybe longer though I've never chanced it) in the summer months & still fire up first turn of the key. During winter's dampness I reduce this to no longer than two weeks, with the same result.

As for battery life I reckon to get around five years from one from a reputable brand, despite the car's low usage.

 

[Harry Bloomfield]

But am I wrong in expecting the car battery to hold enough charge to operate the electronics and start the car for more than 17days on a battery that is only that old?

Normal, is to be able to leave a car parked up, unused, for 30 to 60 days, but that depends on the battery being in good condition and fully charged, when parked up.

I personally, would not leave any modern car that long, without having some means of keeping the battery topped up, in place. I my car, gets a daily 20 minute boost charge, daily, whilst in my garage.

 

[Avocet]

As others have said, they should live a lot longer than that. My wife's 2006 Nissan still had its original battery with Japanese writing on it, when it was written-off in 2019. And also as has been said, should be able to cope with at least a month left standing. Modern cars tend to progressively shut down systems after switching off, so (say) 5 minutes after switching off, some circuits will "go to sleep", whilst others will stay live (radio, perhaps), for maybe half an hour and then go to sleep. Without knowing what the car is supposed to do, it's hard to measure current drain, as popping the bonnet to check the battery, might actually "wake some of the electronics up" again.

 

[Harry Bloomfield]

Without knowing what the car is supposed to do, it's hard to measure current drain, as popping the bonnet to check the battery, might actually "wake some of the electronics up" again.

To avoid that, pop the bonnet open, and put a brick on the sensor. My present car goes into full sleep/minimum load, within 10 minutes, but after being left for four weeks undisturbed, switches the remote control receiver off after a month - then you have to use a key, in the door, to wake it back up.

Leave interior/boot lights on, and they switch off 20 minutes later.

 

[ericmark]

With the smart charger powered from a energy monitor one should see on the PC what power is required to maintain the battery.

I have tried with my clamp on meter, but measuring up to 10 mA is a bit hit and miss, the hall effect used to measure DC needs to be zeroed and so not easy to show.

But simple maths, 48 amp hour battery at 0.1 amp will last 20 days. Although not enough left to restart a car. But my charger at lowest rate is 0.8 amp, and it shows charging around 50% of the so can expect it to be half charged after 20 days.

The problem is the time it takes to recharge, with the hydrometer one can see state of charge, but using voltage not so easy. If it takes a battery 10 days before it accepts a charge after being left abandoned, we can assume it can also take that long to revive a battery that has been repeatedly only half charged.

The charger will not show half charged, neither will a volt meter, the volts will go to 14.4, drop to 12.8 then back to 14.4 many times, each time a little more charge accepted, if one knows the vehicle and battery the mark/space ratio may tell you something, but only real way to be sure fully charged is to leave on charge with a smart charger for 14 days.

 

[bernardgreen]

But simple maths, 48 amp hour battery at 0.1 amp will last 20 days

What will the battery voltage be at the end of those 20 days ?

At what time in those 20 days will the equipment supplied by the battery cease to operate due to low voltage ?

How many amp hours will have been used when the equipment ceases to operate due to low battery voltage.

 

[ericmark]

Never bothered measuring. I know when my e-bike battery is getting low, the hills it will take me up get fewer, but with any battery as it gets lower performance will fall off. But if it starts that's all we need.