Doing a maintenance charge on a seldom used vehicle

[Snagglefoot]

There has been a fair amount written about topping up charges on batteries to keep them in good shape. I have a 2nd car that currently gets used on weekends averaging 40 miles across the weekend. Never really paid attention to this issue but decided to put the smart charger on. The battery is a Ever Start Max closing in on 4 years old. I have a Motomaster smart charger. On starting the charger it immediately ramped up to 2 amps. After a while it increased the amperage to 3.5 amps and the cooling fan came on. Then slowly the amperage came down to 1.3 amps at 2 hrs and when I checked it was 0.3 amps at 7 hrs, 0.1 amps at 10 hrs and finally came to rest at 0 amps and a FUL indicator at 12 hrs. My battery tester then indicated 820 CCA. I take it this battery probably benefitted from the charge but I don’t know if it’s worth it to carry on with this. Any thoughts ? Thanks.

 

[Wrenchturner44]

Yes, I have done the same thing only using a float charger. I have one of the inexpensive HF ones and it works great. I once had an indication that the battery was down significantly (estimate 25%) and the float charger brought it all the way back over about 3 days of time. I am not an expert, but I think it would be better to slow charge seldom used batteries than to use a conventional charger on them occasionally.

The vehicle in question is used similar in the manner you described with yours, and I only put the float charger on it about one per month for a couple of days time or if I get an indication that the battery is indeed in low charge state.

 

[carviewsonic]

Sounds like your battery definitely needed topping up, however, using the car each weekend should keep the battery in good shape. The smart charger your using shouldn't be overcharging, so it could be short trips in cold weather, with defrosters/seat heaters etc. that's running the battery down a bit. Or the car is putting a small draw on the battery when not running. If you don't mind putting the charger on each week, it should help more than hurt anything.
I have a couple Shumacher 1.5 maintenance chargers. If one of our cars has sat for more than 2 weeks or so, I hook up one of the chargers and leave it on overnight or until the indicator light says the charge is complete. I don't leave them hooked up all the time, I think they let the battery voltage drop too low anyway on float mode before charging again.
I replaced the battery in our Honda at ten years, and the one in our '03 PA is six years old and going strong.

 

[JHZR2]

It is pretty well known that car alternators dont truly top up batteries.

Of course, this is a reason why, though we can chase the absolute best charger, "good enough" might be good enough. There are lots of things working against getting the optimal best, and next time you operate, likely it will no longer be topped up. But the one thing that we do know is that the closer to 100% we are, the lower the sulfation, and the better off the battery is.

So batteries will always need topping up, for a number of reasons. And I think you did good.

For vehicles that get a lot of use, so is pretty close to full, then parked for a week, putting in an SAE connector attached to the terminal, and then a maintainer charger is convenient.

What you saw is expected in a nearly full battery. The charger will bump up voltage, resulting in some current flowing, but it will be an exponential decay, and will drop down pretty quick, then stay at a low rate for a long time. Totally normal.

I like that your charger tells you current. That's always interesting from a metrics perspective, because it helps you understand what the battery is actually accepting.

 

[circuitsmith]

I take it this battery probably benefitted from the charge but I don’t know if it’s worth it to carry on with this.

I would do it every 3 months.
That's what I did before getting a solar charger.
I drive once or twice a week, mostly short trips. Even less in the days of COVID.
My last battery replacement was at 9 y.o. Working okay, but didn't trust for a 10th winter.

 

[WylieCoyote]

I do this on on the Mustang, since it's driven once a month, at best. I'm finding that leaving the car unlocked in the garage keeps the alarm system inactive, and produces less drain on the battery. The first time it sat for about 45 days with the doors locked, it took 6 hours of charging to top it off. I think this particular smart charger isn't very aggressive. It has no gauges to tell me what it's doing, just lights.

 

[JHZR2]

I would do it every 3 months.
That's what I did before getting a solar charger.
I drive once or twice a week, mostly short trips. Even less in the days of COVID.
My last battery replacement was at 9 y.o. Working okay, but didn't trust for a 10th winter.

IMO thats a bit too long. Depending upon temperature and how much load the vehicle puts on the battery when "sleeping", the rate of "self discharge" can be pretty high, and 3 months would take a lot of capacity out. Id want to top it off every month, if not just leave a maintenance charger on.

 

[circuitsmith]

IMO thats a bit too long.

Sure, more often can't hurt.
For me, because I park on a city street, it meant taking the battery out & charging it in the basement overnight.

 

[JHZR2]

Sure, more often can't hurt.
For me, because I park on a city street, it meant taking the battery out & charging it in the basement overnight.

Yeah, that makes a difference. Can you disconnect the battery cable for the long sit?

 

[Hermann]

I will throw my old cir 1991 BMW motorcycle changer on my truck when it doesn't get used much. It will charge at 2 amps for a while then slowly tapers and finally goes into float mode. The only benefit I see is the auto start-stop works better (more consistent). Also did this on the Tacoma before this truck and it had a 7 year old battery when it was traded.

 

[circuitsmith]

Can you disconnect the battery cable for the long sit?

Not sure what you mean.
Disconnecting the battery every week?
Don't want to do that. I'd lose my trip odometer data and sound system setup each time.
It used to be enough of an inconvenience every 3 months.
Anyway, the 10W solar panel on the dash brings the battery up to ~13.5V each sunny day.

 

[Duffyjr]

My ctek only has lights but it always takes 14-16 hours before it's done. I usually only use it a couple times a year but with covid and working at home I've done each vehicle four times this year. The AGM in my truck will be five in February and while I've never had it tested it spins that 5.7 pretty good.

 

[JHZR2]

Not sure what you mean.
Disconnecting the battery every week?
Don't want to do that. I'd lose my trip odometer data and sound system setup each time.
It used to be enough of an inconvenience every 3 months.
Anyway, the 10W solar panel on the dash brings the battery up to ~13.5V each sunny day.

Sounded like the vehicle can sit over 3 months at a time. You said it’s hard to charge more often than that because you need to bring the battery in. So Inasked if you can disconnect the battery. Not sure I understood that the vehicle was used weekly. Thought it sat longer in some cases.

 

[circuitsmith]

Sounded like the vehicle can sit over 3 months at a time.

I drive once or twice a week, mostly short trips. Even less in the days of COVID.

 

[JHZR2]

Yeah, missed that I guess.

Disconnecting the battery with a switch might still be prudent.

Ampper Top Post Battery Disconnect Switch, Battery Master Switch Isolator for Power Disconnect Cut Off https://smile.amazon.com/dp/B07JYYXJH7/ref=cm_sw_r_cp_api_glc_fabc_MX96FbVJFAHRC

 

[bluesmokertdi]

There has been a fair amount written about topping up charges on batteries to keep them in good shape. I have a 2nd car that currently gets used on weekends averaging 40 miles across the weekend. Never really paid attention to this issue but decided to put the smart charger on. The battery is a Ever Start Max closing in on 4 years old. I have a Motomaster smart charger. On starting the charger it immediately ramped up to 2 amps. After a while it increased the amperage to 3.5 amps and the cooling fan came on. Then slowly the amperage came down to 1.3 amps at 2 hrs and when I checked it was 0.3 amps at 7 hrs, 0.1 amps at 10 hrs and finally came to rest at 0 amps and a FUL indicator at 12 hrs. My battery tester then indicated 820 CCA. I take it this battery probably benefitted from the charge but I don’t know if it’s worth it to carry on with this. Any thoughts ? Thanks.

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While your car is parked a small current (milliamps) is being drawn to maintain the clock, engine computer etc.; inevitably the voltage will drop.

I have the identical charger and it works great, I put my occasionally used car on the charger overnight about once every 2 weeks

 

[NH73]

Maybe it is a good idea to put a charger on a battery every winter and also when you buy a new one. It seems batteries can all of a sudden just start failing with little warning anymore.