Recharging car type batteries when you have lots of time

[Donald]

Asking for both normal flooded and AGM

If one has weeks or months to recharge is it better to recharge at low like 2 or 3 amps or high at 6 or 8 amps?

 

[ripcord]

For healthy batteries I doubt it makes much difference.

 

[JeffKeryk]

I've had the NOCO 1A fail on 2 vehicles, both with excellent batteries. I bought a 4A (I think) from Costco; I will check it next week when I'm at our other place.

 

[Donald]

For healthy batteries I doubt it makes much difference.

But BITOG philosophy is to discuss everything getting down to the tiniest most insignificant detail?

 

[eljefino]

Lead acid batteries like getting charged at 1/10 their amp hour capacity. Trickle charging at less than that works as well, but this could be for the convenience of the charger. Imagine an emergency exit light that had to have a beefy charger and timer circuitry instead of a simple trickle charger.

 

[LongTime_Lurker]

I would just use a microprocessor controlled charger with the proper modes for your battery type. You can use an inductive clamp meter on one of the leads if you really want to monitor the charge rate. Set it and forget it!

 

[Donald]

I would just use a microprocessor controlled charger with the proper modes for your battery type. You can use an inductive clamp meter on one of the leads if you really want to monitor the charge rate. Set it and forget it!

I have a Battery Minder. Is microprocessor controlled. But you can set it for 2 or 4 or 6 amps.

 

[vpr5703]

On full size car batteries I charge at 10 amps on my charger. I monitor heat generated by the battery, and it barely warms above ambient. So I figure it's OK. When I start my car and watch my OBD2 data I see 40-50A of output from the alternator and it slowly settles down to about 20A after the battery recharges. So I figure in my case 10A charge is perfectly fine.

 

[Donald]

Lead acid batteries like getting charged at 1/10 their amp hour capacity. Trickle charging at less than that works as well, but this could be for the convenience of the charger. Imagine an emergency exit light that had to have a beefy charger and timer circuitry instead of a simple trickle charger.

My batteries are 80 to 95 amp hours so 8 amps seems about right. And that is the max for this model Battery Minder.

 

[2heeldrive]

Too high a charge rate is much worse than too low. 2-3 amp should fine.

 

[ripcord]

Too high a charge rate is much worse than too low. 2-3 amp should fine.

According to the Battery University site, battery manufacturers say charging a lead acid battery at a "C-rate" of 0.3 is not harmful. To get the .3 C-rate of a battery, you just multiply the capacity of the battery in amp/hours by .3. So if you have a typical 90 amp/hour truck battery, 90 X .3 = 27, so 27 amps during the bulk charging phase would not be a problem. In fact, most cars will charge a dead battery at higher current levels than even that which is why they say to avoid letting the alternator charge a dead battery as it can overheat the alternator.

BU-403: Charging Lead Acid

BU meta description needed...

batteryuniversity.com

 

[Donald]

According to the Battery University site, battery manufacturers say charging a lead acid battery at a "C-rate" of 0.3 is not harmful. To get the .3 C-rate of a battery, you just multiply the capacity of the battery in amp/hours by .3. So if you have a typical 90 amp/hour truck battery, 90 X .3 = 27, so 27 amps during the bulk charging phase would not be a problem. In fact, most cars will charge a dead battery at higher current levels than even that which is why they say to avoid letting the alternator charge a dead battery as it can overheat the alternator.

BU-403: Charging Lead Acid

BU meta description needed...

batteryuniversity.com

Good to know. That's a lot higher than most 110v plug in chargers can put out.

 

[bonjo]

for lead batteries, the slower the charge the better: low current.
I use my motokbike chargers rated 0.8 & 1 amp for the car as well. It take longer of course.
Smart chargers switch off if the battery does not reach a certain level within a time limit.
So to charge a large capacity flat battery with low current smar charger might need few rounds

 

[berniedd]

Here's my experience with very slow charging: In 2013, my daughter left my Honda CRV in the parking lot of the hospital where she works, for 4 days. Unfortunately she had left the dome light on. Of course, this completely discharged the battery (45 amp-hours capacity as per Honda owner's manual). The battery was 7 months old at the time. I went there, removed the battery and took it home. All I had was my charger that was nothing more than a homemade rig of a tiny 1/2 ampere stepdown transformer to 12 volts on open circuit, a bridge diode rectifier, and a smoothing 1000 microfarad capacitor. (I use this to power my electronics projects and experiments.)
I connected this crude power supply to the dead battery for a full 7 days. I measured a 1/4 ampere (250 milliamperes) of charging current with my digital multimeter. At the 7th day mark she really needed the car so we both went to the parking lot and reconnected the battery. The engine started normally on the first try. After that, it lasted another 3 years before it needed to be replaced. So I guess the short lived fully discharged condition did no serious effect on battery life.

Revisiting the charging, the math goes 7 days X 24 hours/day X 0.25 ampere = 42 ampere-hours total energy returned to the battery.

Anyone trying something like this on a battery left discharged for a longer time may or may not get similar results. However, a 1/4 ampere charging current can be safely left connected for weeks to a regular car battery.

 

[Donald]

Here's my experience with very slow charging: In 2013, my daughter left my Honda CRV in the parking lot of the hospital where she works, for 4 days. Unfortunately she had left the dome light on. Of course, this completely discharged the battery (45 amp-hours capacity as per Honda owner's manual). The battery was 7 months old at the time. I went there, removed the battery and took it home. All I had was my charger that was nothing more than a homemade rig of a tiny 1/2 ampere stepdown transformer to 12 volts on open circuit, a bridge diode rectifier, and a smoothing 1000 microfarad capacitor. (I use this to power my electronics projects and experiments.)
I connected this crude power supply to the dead battery for a full 7 days. I measured a 1/4 ampere (250 milliamperes) of charging current with my digital multimeter. At the 7th day mark she really needed the car so we both went to the parking lot and reconnected the battery. The engine started normally on the first try. After that, it lasted another 3 years before it needed to be replaced. So I guess the short lived fully discharged condition did no serious effect on battery life.

Revisiting the charging, the math goes 7 days X 24 hours/day X 0.25 ampere = 42 ampere-hours total energy returned to the battery.

Anyone trying something like this on a battery left discharged for a longer time may or may not get similar results. However, a 1/4 ampere charging current can be safely left connected for weeks to a regular car battery.

A real charger with a desulfate function might have helped get the battery back to top condition after it was let run to dead.

 

[f355spider]

There is a quote in the instructions for use on the Optima batteries website (no longer a fan of Optima after three leakers) about charging and they say "low and slow" is best.

• Low and slow is best. A low-amp charger (one to 12 amps) is generally the best choice for charging any lead-acid battery. It's quicker to charge at higher amperage, but it also can generate a lot of heat, which reduces the life of a battery, just like the heat of summer.

 

[f355spider]

I have a Battery Minder. Is microprocessor controlled. But you can set it for 2 or 4 or 6 amps.

I have one of those to, with 2,4,8 amps....I generally use it on the 2 amp setting, but use the 4 amp when maintaining two batteries at the same time (which is the Battery Minder recommendation). One of my BMWs has two AGMs, one in the engine compartment and one in the trunk.

I bought this accessory: https://www.batteryminders.com/batt...-battery-connector-w-ring-terminal-connector/

The ring connector goes to the charging terminals in the engine compartment (which goes to the battery in the trunk) and the ring connector set that came with the battery minder goes on the battery in the engine compartment.

 

[Donald]

I have one of those to, with 2,4,8 amps....I generally use it on the 2 amp setting, but use the 4 amp when maintaining two batteries at the same time (which is the Battery Minder recommendation). One of my BMWs has two AGMs, one in the engine compartment and one in the trunk.

I bought this accessory: https://www.batteryminders.com/batt...-battery-connector-w-ring-terminal-connector/

The ring connector goes to the charging terminals in the engine compartment (which goes to the battery in the trunk) and the ring connector set that came with the battery minder goes on the battery in the engine compartment.

I solved that problem with three Battery Minders. I might have two of the older ones also.

 

[f355spider]

I solved that problem with three Battery Minders. I might have two of the older ones also.

Its easier to make a single connection to the car than multiple. I have several battery tenders as well. Two each Battery Minder, two each Granite Save a Battery, as well as a couple Griots Garage and a Battery Tender.

 

[Donald]

Its easier to make a single connection to the car than multiple. I have several battery tenders as well. Two each Battery Minder, two each Granite Save a Battery, as well as a couple Griots Garage and a Battery Tender.

I personally think of any battery charger companies Battery Minder has figured out desulfation as best as possible. It's listed on their website. Basically you charge the battery then test the battery then let keep the Battery Minder connected for another day and retest allowing for surface charge. Keep doing that and as long as it keeps improving you keep the Battery Minder connected for another day then retest. It can take awhile.

If you don't get it back to a usable battery then time for a new battery. No panacea.

My 3 batteries are from my boat and I have no access to the boat from mid December to early April and boat has no AC power available. So they need to come out and be brought home.

As I get older (70) it sure seems the batteries get heavier.