Keep your car battery charged!

[ERD50]

Your car battery may be very low if your driving habits have changed with all the COVID shutdowns/restrictions (or any other reason you are driving less). Check it and keep it charged! Here's what happened to us:

DW was going to go shopping Sat AM, and her car wouldn't turn over, just "click-click-click". Battery will be 6 years old next January, so about time to replace anyhow.

But I suspect the main issue is the short and infrequent trips have just not kept the battery charged. We use my car for longer trips. I measured and it was at 11.7V, which is very low, but maybe not a bad cell.

So I wondered about my car (3 YO original battery), and it was at 12.0V which is also very low (and I had some extended trips, ~ 40 minutes, a few weeks ago), but it started, so we did our shopping together.

Some notes on Battery Voltage vs capacity (measured after battery has 'rested', off the charger, for > 20 minutes):

12.70V ~ 100% capacity
12.48V ~ 75%
12.24V ~ 50%
12.06V ~ 25%
11.89V ~ 0%

Dropping below ~ 10.2V can permanently damage the battery.

So I put our ancient simple non-electronic/non-smart charger on hers for a few hours Sat evening, but didn't want to leave it overnight unattended. This morning, it measures ~ 12.2V. I wondered, how long do I need to keep this charger on to reach full capacity?

Well, the RC25 rating is 85 minutes, so that's 25 Amps @ 85 minutes, which is ~ 35 Amp Hours (25⋅85/60). I measured the charger current after it was on for 10 minutes or so at ~ 1.3 Amps. So that indicates it would take ~ 35/1.3 ~ 30 hours for a full charge - far more than I would have thought.

So I'm going to leave it on and check it before dinner to see where I get, then do my car tomorrow. Oh, I did plan on just buying a new battery when we were out Saturday, but the place I go to was closed for the Labor Day w/e (with no note on their website!). While I suspect this battery will be OK after a full charge, I'll still replace it before winter as a precaution.

So not a bad idea to check your battery voltage to avoid a surprise. Fortunately, this happened at home which made things less stressful.

-ERD50

 

[O2Bfree]

Good point, all the electronics on cars these days can really draw the battery down. We've been having this trouble with my mom's car since she stopped driving last year. We kept the car at our house for awhile and used it to go to her place and for occasional errands, but during the riots in Seattle (30 miles away, mind you) she insisted on keeping the car at her place in case she needed to make an escape. She's nearly blind in one eye and had no idea where she'd drive to, but we couldn't reason her out of that. We do use it when taking her places more than about 10 miles away, which is only a couple times a month. Saves us gas and miles on our car, I guess. But the last time we needed to take her into Seattle, the battery was dead. We jumped it later, then brought it to our house and put it on the trickle charger. Need to keep a closer eye on it and bring it over for charging as necessary.

 

[target2019]

I bought the BEATIT B10 QDSP 800A Peak 12V Portable Car Lithium Jump Starter as recommended on another thread.

I'll have to go out and check the voltage with it.

 

[Souschef]

The first time I took my car out after the lock down, I had the same problem, a dead battery. Fortunately, my charger has a jump start setting, and it worked well.
Fortunately, we are in Southern California, so a cold start was not a problem.

 

[ERD50]

I bought the BEATIT B10 QDSP 800A Peak 12V Portable Car Lithium Jump Starter as recommended on another thread.

I'll have to go out and check the voltage with it.

And if your car battery is low, I assume you could use that Jump Starter to simply top off the car battery with a slow/moderate charge? That would be better to be proactive, rather than responding to a jump start if it gets really low. As I mentioned, if the car battery drops to below ~ 10.2V, there can be permanent damage to the battery.

Let us know what you find.

-ERD50

 

[bjorn2bwild]

Some notes on Battery Voltage vs capacity (measured after battery has 'rested', off the charger, for > 20 minutes):

12.70V ~ 100% capacity
12.48V ~ 75%
12.24V ~ 50%
12.06V ~ 25%
11.89V ~ 0%

As usual, good information.

I was not familiar with this heuristic - I tested the 3 year old AGM battery in my seldom driven truck - 12.55V with a digital meter, the scale on the analog meters are not granular enough to make a clear call.
I do put the battery on a charger when it will be sitting more than a couple weeks - either PV powered or the digital float charger.
I have read the float chargers will only maintain a battery, a conventional 'buzz box' or three stage charger is best if the voltage gets below a certain level(?)

PS - OK, I think I read that somewhere in this related thread over at bogleheads -

https://www.bogleheads.org/forum/viewtopic.php?f=11&t=323191

 

[Sunset]

Last night I went out to pick up a pizza, and DW's car with a 5.5 yr old battery was slow to start.
I had not driven it in a couple of weeks.
This battery is getting weak, and I had to charge it up a couple of times due to lack of driving.
Soon will be time for a new battery, which I'll put in our "newer" car, and move it's battery to DW's (the to be moved battery is only 1 or 2 yrs old).

I figuring DW will trade in her 23 yr old car once it gets too old so don't want to trade away a new battery.

 

[target2019]

Without key I got 12.3V. With key on I got 12.0V. So it's marginal.

I also noticed the lithium jump starter does not charge itself (3 out of 4 LEDs).

 

[firemediceric]

For my diesel truck with two big batteries, 850 CCA, I purchased two of these solar chargers with a splitter to run them both through the 12v. power outlet in the truck. They seem to do the job on a truck that get's driven once every 10 to 14 days or so.


https://www.amazon.com/gp/product/B07ZQ85PQJ/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

 

[RunningBum]

My Miata used to do pretty well even if it sat unused for 2-3 months, until I put a new radio in. It must draw a little bit of a charge because it can no longer sit for a week or so. I bought this trickle charger that has worked great the last 1.5 years. https://www.amazon.com/gp/product/B010NRKERI
I keep it connected to the Miata unless I'm pretty sure I'll be driving again in a few days.

A few years back I bought an Anker portable jump starter, that also works great as a mobile USB charger. It's no longer carried by Amazon but it still does the job for me. I have a calendar reminder to recharge it every 3 months, or proactively if I'm taking a driving trip.

 

[Major Tom]

Yes, 6 years is rather old for a starter battery! My only vehicle is a camper van built on a Ford E350 chassis. The starter battery is fitted with a knife switch, which is very useful. Whenever I am not driving it, I use the switch to disconnect the battery. In a van this old (1993) there is probably not a lot of electronic stuff that is causing a residual draw, but completely disconnecting it when not in use can only help.

I suspect that your DW's car is parked inside but, if outside, a small solar panel parked on the dash and plugged into the cigarette lighter could help keep it topped up during long periods of disuse.

 

[audreyh1]

DF’s truck doesn’t get driven very often. We attach a battery charger once it’s been two weeks.

If we know it’s not going to be used for a while we disconnect the battery.

 

[Freedom56]

My wife's 370Z wouln't turn over about a month ago. I put a battery charger on it and it was drawing 5 amps after it was connected. After 24 hours, it was drawing less than one amp. The car started and we have not had any issues since. We just make sure that we use it at least once a week.

 

[W2R]

Back in March and April, our mandates specified that we couldn't leave home except for absolute necessities. The streets were empty and local authorities were stopping people who they suspected were violating the mandates. Like others here, we went for weeks without driving anywhere.

We were concerned about our car batteries. Once a week I ran my car's engine while it was sitting on the driveway, for long enough to keep the battery charged. Frank did the same with his car.

Now that mandates have relaxed, we go on pleasure drives nearly every day (plus now we can drive to our restaurant for lunch) so no run down batteries. My battery is just five years old so it is still in pretty good shape.

If we had a problem, Frank has one of those devices that plugs into the wall and can get the car started, but we haven't needed it for years.

 

[mystang52]

I love "my" SUV, and dislike driving DW's sedan. Whenever we go out together I always drive. I make it a point to mix in a fair amount, but still less than half, of driving with DW's car for this very reason.

 

[Koolau]

I used to leave my mainland car "abandoned" in my back yard. Battery was at least 3 years old when I started this non-recommended practice. No one started it and no one charged the battery for 9 months. It started that way for 3 years (sounded like a diesel, but the battery was fine.) When I could no longer open the passenger door (broken lock - cost to replace more than value of car) I virtually gave the car away. It "died" a year later when manual trans froze up due to never having been maintained (Oops! My bad.) But the battery was still good - a cheapo from Sams IIRC. YMMV

 

[Bamaman]

With 4 cars/trucks and 2 boats, I sometimes will find a slightly run down battery. I keep a set of jumper cables and a good battery charger handy at all times.

 

[jimbee]

A Battery Tender Jr., or similar battery maintainer, can be a good idea if you don't drive your car regularly. $25 at Walmart or Amazon.

 

[Chuckanut]

I try to take my car out at least once every other day for a short trip. I also do one long trip (30+ miles) each week whether I need to or not.

After a friend of mine spent several hundred dollars getting the mice out of his car and repairing the damage they did, I decided driving a bit even when not necessary is a good idea.

 

[zedd]

We've been driving less since the onset of the [-]zombie apocalypse[/-] pandemic. DW's Tahoe battery wasn't holding a charge. Isolated it to a vampire draw from the stereo. Temporary fix was to remove the "accessory" fuse. Well that caused the turn signal "clicker" to stop working. Turns out the "clicker" sound is piped thru the stereo speakers

 

[Montecfo]

I rotate which car I drive for errands. Did get a new battery for the old Camry, which we call the "mule".

And I keep jumper cables handy.

 

[NateW]

...Some notes on Battery Voltage vs capacity (measured after battery has 'rested', off the charger, for > 20 minutes):

12.70V ~ 100% capacity
12.48V ~ 75%
12.24V ~ 50%
12.06V ~ 25%
11.89V ~ 0%

Dropping below ~ 10.2V can permanently damage the battery.

-ERD50

Very good information, thanks for posting ERD50. I checked our Toyota RAV4, which has not been driven in about a week and a half. Used my 1985 vintage Radio Shack digital volt meter. Got 12.35 volts. I then hooked up a 1970s vintage Montgomery Wards 10 amp/2 amp battery charger on the 2 amp setting and let it charge for a couple hours. Disconnected the charger, waited half an hour and measured battery voltage again. Got 12.75 volts. Then turned the interior light on for a few seconds and then off and checked again and got 12.67 volts (I read somewhere long ago you can check battery state after charging by measuring no load voltage, but need to first provide a slight current draw to remove the surface charge after charging).

 

[ERD50]

Somewhat of a co-incidence, but I started thinking about our car batteries again, and this post is just over a year old, so a good time for an update/reminder.

Since we moved this spring, we can do a lot of our shopping at the very nearby center, just 0.9~1.1 miles away. So that's a high % of very short trips, DW will sometimes walk if the weather is nice and she only needs a few things.

I checked mine (which is in the garage) by opening the hood the night before and letting the battery 'rest'. In the AM, I got ~ 12.38V, so maybe ~ 60% charge. Not bad, but not great. DW's was a little lower, and I didn't give a full rest, since she's parked outside until we get the garage more organized.

Put on the ancient charger I inherited from my FIL, it settles down to ~ 1~2 amps after a while. I left it on for about 8 hours and got to roughly 12.60 the next AM after the 'rest', which is ~ 90%. I also charged DWs for about 5 hours, I need to check and probably add some charge time.

REMINDER: If your battery is low, just "taking it for a long drive" isn't going to do much. It takes a LONG time to bring a battery back up ( I gave a rough estimate of ~ 30 hours from 0% to 100% in the OP).

However, a longer trip every week will probably help to replenish what was drained from starting and the phantom drain when parked. I'm seeing ~ 75mA mentioned at typical for modern cars. So a week of sitting would be 12.6 AH, and my battery is ~ 35AH based on the RC25 rating (but would be higher for small drains), but that's still maybe 25% discharge in a week? If the battery is accepting 2A average while charging (I see it drop from ~ 6A to ~1.2A over the course of a few minutes), that's still ~4~5 hours of driving a week to keep it charged (not counting starting current, but 2 seconds at 200A is very small in amp-hours).

These are very rough, first approximation numbers. A very low battery will also draw more charge current for a longer time, so that offsets all this somewhat. And can get you to a charge level that won't leave you stranded, unless it's in cold weather. I'd guess that even a 25% battery will still turn over an engine OK under good conditions.

Bottom line, I plan to check and probably charge up our cars about every 3 months.

Very good information, thanks for posting ERD50. I checked our Toyota RAV4, which has not been driven in about a week and a half. Used my 1985 vintage Radio Shack digital volt meter. Got 12.35 volts. I then hooked up a 1970s vintage Montgomery Wards 10 amp/2 amp battery charger on the 2 amp setting and let it charge for a couple hours. Disconnected the charger, waited half an hour and measured battery voltage again. Got 12.75 volts. Then turned the interior light on for a few seconds and then off and checked again and got 12.67 volts (I read somewhere long ago you can check battery state after charging by measuring no load voltage, but need to first provide a slight current draw to remove the surface charge after charging).

I've read anything from a couple hours to 24 hours rest. And even the 75mA drain could pull off some of that charge. But I think for general checking, something like what you did is probably close enough to remove that surface charge and get a usable reading. We're not trying to get down to exact %, just ballpark. I may experiment with this, and see if a couple seconds of headlights on and a 10 minute rest is as good as an overnight rest.

-ERD50

 

[SecondCor521]

^ Wouldn't the amount of time to recharge a battery by driving be dependent on the alternator, not the charger? That is, your 30 hour estimate is based on an external charger (I think), but recharging on a long drive would be based on the alternator...?

Just reading along for interest, mostly. I mostly can't grok electricity stuff.

 

[brett]

The battery on our Honda was 10 plus years old when I replaced it last year.

For the past 8 years we have spent 3 winter months travelling. I have routinely pulled the battery out rather than have it sit in an unheated garage. And changed the insurance to fire and theft only.

Do the same with our summer car when we take it off the road in the fall.