# Is it possible to fully charge a 12V lead-acid traction battery using a car battery charger?

I got a 45Ah 12V traction battery for my experiments and I was assuming that I can recharge it using a normal car battery charger (the main difference between 12V car starting battery and 12V lead-acid traction battery being that traction battery is more deep-discharge resilient and support way more cycles).

But there is some information label on battery that say there are 2 different charging methods for 2 different use cases, which confused me:

• Stationary use: charging voltage 13.6 - 13.8V
• Cyclic use: charging voltage 14.5 - 14.9V

Max charging current: 13.5A

The microprocessor controlled car battery charger I have is using 4A charging current, so I guess it should work, just might be a bit slower, but I am not really sure how the lead-acid battery charging process works. Is that charger going to recharge the battery until some predefined target voltage, or is it using some sophisticated calculation to figure out if battery is really charged to 100%?

I would like to avoid car charger stopping the charging process at, say, 50% of actual battery capacity, because I noticed that different 12V lead-acid batteries, seem to have different voltage at "full charge". How is this full charge determined? Is this car battery charger going to work for this, or do I need some special charger?

• Chargers with some manner of control circuit do indeed use some intelligent calculation/table to see when the battery is charged given the specific chemistry. Each chemistry will have its own typical charge/discharge curve. – Lundin Aug 9 '19 at 8:13
• Is it mechanism described anywhere? I would like to understand how it works (eg. how can you determine if lead-acid battery is 100% charged) – Petr Aug 9 '19 at 8:22
• The simple statement is that charging at 4 amps instead of 13 amps means that it will take about 3 times longer to charge, but it also depends on the state of charge when you begin charging. A good method of assessing the state of charge is to use a hydrometer. see www.powerstridebattery.com/blog/what-is-a-hydrometer-and-how-do-i-read-one/ – Solar Mike Aug 9 '19 at 8:57
• You need to read the charger's documentation, particularly regarding charging cycle cutoff voltage. – Brian Drummond Aug 9 '19 at 10:34
• Re, "I noticed that different 12V lead-acid batteries, seem to have different voltage at 'full charge.'" How much difference? And, what told you that the batteries were "fully charged?" – Solomon Slow Aug 9 '19 at 15:15