The Stovebolt Site Forums The Shop Area The Electrical Bay Can you trickle charge more than one battery at time?

Can you trickle charge more than one battery at time, using one battery trickle charger ?

Like two 12 volt batteries paralleled together.
or two 6 volt batteries paralleled together.

You'll need a charger with more amperage capacity than the average trickle charger- - - - -maybe one with a max output of 10-15 amps. Most real trickle chargers have a capacity of 5 amps or less. The battery with the lowest specific gravity will hog most of the charge current until the one with the lower state of charge comes up to the level of the higher-charged one.
Jerry

That is what I thought.
The charger I have is a walmart Special and Schumacher xm1-5 Manual
I have two 12v batteries side by side and have been charging one for a week then the other for a week.
Then back to the other, so on and so forth.
Thought there might be a better way.

What's the specific gravity of the cells on both batteries? Once a cell gets up to 1.265 or so, more charging doesn't do any good. Individual cells should be within 20 points of each other, like 1.250, 1.265, etc. The closer the better. If all the cells are above 1.250, the battery can be load tested effectively. Load the battery to 1/2 its Cold Cranking Amp (CCA) rating for 15 seconds. For instance, a 500 CCA battery gets loaded to 250 amps for 15 seconds. With the load still applied, the terminal voltage should not drop below 10.6 volts. Without a load test, other indicators of battery condition such as open circuit terminal voltage are pretty much worthless.
Jerry

What's the specific gravity of the cells on both batteries? No clue
A lot of what you are asking about is above my pay grade.
Both batteries are sealed.
How do you do a gravity test on a sealed battery?
I really don't have test equipment to do a load test.
I use to go to the Sears automotive store to do a load test but they closed up.

I might be charging junk batteries. But the charger I am using says it can detect a sulfated battery.

I've got two older batteries that I don't trust in a vehicle powering the lights and jack on my car hauler. I have them daisy chained together with a trickle charger all the time.

Do they maintain a charge?

They maintained enough charge to run the jack after I forgot to plug the trickle charger in for a month.

Sealed batteries can't be gravity checked. If you've got a vehicle handy to install the battery into, try spinning the starter for 15 seconds with the ignition disabled so it won't start. After that time, while still cranking, the battery terminal voltage of a good battery shouldn't drop much below 10 volts. It's a quick and dirty shade tree load test, but it works pretty well.
Jerry

I will give it a try.
I use to park the vehicle close to the garage door so the headlights would reflect off the garage door.
Then I would crank the engine over and watch how much the headlights would dim down while engine was cranking.
If the headlights would dim down to nothing I would suspect the battery was no good or there was a bad connection.

FWIW: Per advice given here, I fully discharge an almost new 12 volt battery that’s awaiting me to finish beating a 1957 Chevy two door Belair back to life. I do it with a tail light bulb on every other month. I have several trickle chargers and connected one to the discharged battery. Several days later I went to disconnect the charger only to find it was kaput. I’m not for certain, but I believe the charger could not handle a fully discharged batter and the current limiting section went south. The battery was fully charged and in good shape after I charged it back up with a regular charger set a two amps.
These new fan dangled 12 volt batteries remain a mystery to me. My cars are 6 volt and will stay that way.

A friend had a battery shop for a couple decades starting in the early’70s. They hit all the service stations, garages and all other places that installed batteries in all the towns in several counties.He bought the old batteries for scrap price’s. Batteries that looked good went on a set of shelves that would hold 20 or so. A custom made daisy chain wire (think old time string of Christmas lights) with small nails wired to the main harness was used to slow change all the battery’s at once (the nails were tapped into the post). All the caps were off and any with non bubbling cells after a day or so were pulled and sold to a lead recycler.

Batteries that accepted a charge were cleaned up and sold as rebuilt batteries. When in fact they were good batteries to start with that just needed a change.

So yes to the OP’s question along with the good advice above. The Battery Shop did rebuild batteries but not for little cars/trucks.

Beltfed, the instructions on my trickle charge say that the battery must have a "full charge".

I believe a battery tender of at least 4 amps can charge a dead battery and then maintain the charge. Smaller than that all bets are off and you need a proper battery charger to bring it back up.

The best "econony" charger I've found is the Schumacher unit that has a 2/10/80 amp selector. The 80 amp setting is labeled "boost" and is only used for short bursts of heavy charge to wake up a totally dead battery. Walmart sells a generic charger that closely resembles the Schumacher, and is probably their item with a "house brand" relabel. Fortunately, real battery chargers aren't expensive. The big box-shaped ones on wheels usually cost less than $200.00, or close to half that price when they go on sale. "Buy once- - - -cry once!"
Jerry

That is a great backwoods test for those of us without battery load testing equipment. Thanks Jerry.

I have used jumpers to keep a second battery on a battery maintainer. I works.
I have also used Harbor Freight $5 chargers and they work well. Have been using them for 20 years.
You have to have a charged battery to start with, when using a maintainer charger.