Automotive → Battery charger voltage

What should be the charger output voltage?

Fast or float?

I have a Schumacker 6 or 12 volt 2/15/125 amp charger it probably over 20 years old. I do not know what type it is. With out it being connected the battery it reading 10.5. The battery went up to 12.6 ok. So I guess it working ok. What type of charger should i get for normal charging of a regular lead adic battery? Thanks

The old chargers are unfiltered, rectified AC. Most meters won't measure it right. When charging, it will probably be a series of pulses (charging only during the peak of the AC cycle.)

Fast charging is 13.8 to 14.4V depending on how fast you want to charge and how much the battery can handle.

Float chargers are 13.2 to 13.6V.

Which would be the best to buy?

It depends what do you want to do with it. Your old charger is probably fine to charge a discharged or dead battery, or jumpstart a car, but you should not leave the charger on a battery unattended (unless it's in the 2A setting) for any significant amount of time. But even at 2A, you still need to check it periodically and remove when the battery is fully charged.

When you measure your old charger, measure it with both AC and DC settings.

Float chargers usually have a very small rating (0.5A .. 2A) but they can be left connected indefinitely because they are designed not to overcharge the battery. However, they may not be able to charge dead batteries, or it can take a very-very long time.

Most newer chargers are now electronic, and they only work when they are connected to a battery that is not completely dead.

Ok thanks. How good are the schumacker chargers that suppose to shut off automatically?

I have a Schumacker 12 volt with switch for conventional batteries and low/no maintenance/deep cycle. It is a 10 amp model and is automatic.

Just now: Checking the output voltage on the charger, am getting 10.7 volts on either setting. The reading is steady. Of course the amp meter on the unit is at 0 amps. Do not have a discharged or other battery to hook it to and then check voltage dc.

Have used this unit on deep cycle, low maint., convential in all kinds of conditions. Used on Tractors, Bobcat, ATV, Trucks, old vehicles, new vehicles, deep cycle batteries from those scooters people ride on [got those free from neighbor and used them for portable 12v lights].

The Auto feature works great, have forgot that battery hooked up and had it connected for a week or so, more than once with no damage. Did that a couple of times to one of the Bobcats, especially in winter at freezing temps. The battery in it gets a good workout with many start/run/shutoff cycles per day. When I sold it, it had the original battery and it was 7 years old.

It is probably around 25 years old and made in US.

hth

Schumacher chargers are very reliable, and I recommend them.

If the battery was reading about 10V, it could have a shorted cell (a fairly common issue). If it charges up to 12.6V or so, let it sit for a day or two (with the terminals disconnected). If it sags back down to the 10V range, it definitely has a bad cell.

Most Midtronics brand battery testers (if you know someone who has one) have a shorted cell detection feature- this will tell you right away, without having to wait to see what the battery voltage does over time.

That's a dead battery. Replace it.

Sorry the charger was reading 10.5 not the battery. But it charged the battery to 12.6 volts. I bought a new battery and ordered another charger.

For storing lawn batteries, deep cycle, or other types when not being used, I recommend a Battery Tender. It keeps them topped up and won't overcharge. Leave it hooked up 24/7.

Guess what I got my new Schumacher charger today. Took it out the box and the selector switch does not work. hortnut posted that he has a Schumacker for 25 years. and it is still working.
I'll be taking it in to autozone and getting a refund and have them to special order one for me. I'll still will stick with Schumacker. One bad one does not bother me.

That's just my curse....

lol