Originally Posted by slybunda
Originally Posted by wrcsixeight
The battery accepts as many amps as it wants at the system voltage reaching the battery terminals, upto the maximum output of the charging source.
i have read from here:
https://www.impactbattery.com/blog/2017/05/how-fast-can-i-charge-my-car-battery/ and here:
https://batteryuniversity.com/learn/article/charging_the_lead_acid_battery
that charging car battery with high ampage is not possible since battery can blow up.
so i dont get how for example a 70 amp alternator can dump all its current into a battery in one go, it would cause the battery to heat up considerably and blow up.
most of those websites i have checked say that charging lead acid batteries should be no more than 20% of the ah rating, most suggest 10%. so a 50ah battery should be charged at 5amp or so.
nthach's post above makes sense that the cars alternator/control module needs to be programmed to work with a battery that accepts a higher charge rate.
so what happens if you put an EFB or AGM battery in an older car that was designed to work with just a normal flooded battery? does it charge at the same rate as the flooded battery or will it actually charge up faster?
It comes down to resistance.
Vt=Voc+I*R
Vt (voltage @ terminals) = Voc (open circuit voltage, what the battery would measure if totally disconnected and left alone) + I (current) x R (resistance of the battery).
In other words, the voltage you observe is based upon the electrochemical potential, which varies with state of charge, and the resistance of the battery, for any current pushed in or out.
You can electrolyze water into hydrogen and oxygen if you apply the right voltage.
So remember above. If you give a certain voltage (Vt) from the alternator, the amount of current (I) that will flow is based upon the state of charge (Voc) and the resistance of the battery (R). The alternator is regulated so that the voltage doesn't go sufficiently high and electrolyze water into an explosive gas mixture (hydrogen and oxygen).
For a given Voc, and for a given R, both parameters you have no control over, the only way to charge faster/higher/harder (ie more I), is to up the voltage, Vt. Get it now? Push Vt too high to allow the current to flow, and then you'll electrolyze the water and make an explosive gas. Too much gas in a flooded (unsealed) battery, and it will flow out and away. Too much in an AGM and it will vent, which you dont want to happen.
Hope that makes sense...
Some claim that you should charge harder/higher. But recall also that P=I^2 R, so the battery will heat up with the square of current, times the resistance. Heat is what causes damaging side reactions and degrades batteries. Sometimes there is something to be said about charging with more over potential, even if limiting the current in. But in general, the more gentle and easy you charge a battery, the better off you are (assuming you do indeed fully charge it).