Higher battery cranking amps, less voltage drop?

[ajgraz]

Here’s a question I can’t seem to find a straight answer to:

Assuming full charge, same battery age and condition, temperature, etc., etc., will a battery with higher cranking amps experience less voltage drop when starting the same motor than a battery with lower cranking amps?

 

[GA_Boater]

No. It just will crank longer before going dead. Voltage drop is a function of the length, gauge and condition of the cables and connectors.

 

[sam am I]

Depends............GA is right if you're talking/considering only external resistance leading to the load (starter), all of which (Rs-ext total) will be the same regardless of what type battery is used, therefor the voltage drop across a constant external resistance will remain constant for the same load (starter).

However, different batteries can have different internal resistance (Rs-int total) and even a very small 5 mΩ (0.005 ohms) difference in internal resistance between the two different types of batteries can make for example, a voltage drop difference of 1V between batteries @ the same 200 amps starter load..........You'd have to look at the spec's of the batteries at this point.

 

[ajgraz]

Sam am I,

Good info. So, does that mean that if battery A had an internal resistance of 25 to 50 milliohm (typical numbers I’m seeing on lead acid), and battery B had only 2.5 milliohm (number I’m seeing on good AGMs), then battery B would experience only 1/10 to 1/20 the voltage drop on the same starting draw, based on V=IxR?

 

[Scott Danforth]

Internal resistance is such a small amount of typical voltage drop.

Typical voltage drop issues are bad connections and undersized cables

A bad connection can add hundreds of ohms of resistance. Bad grounds and loose hardware adds to that.

 

[sam am I]

Sam am I,

Good info. So, does that mean that if battery A had an internal resistance of 25 to 50 milliohm (typical numbers I’m seeing on lead acid), and battery B had only 2.5 milliohm (number I’m seeing on good AGMs), then battery B would experience only 1/10 to 1/20 the voltage drop on the same starting draw, based on V=IxR?

Absotutely!, (perhaps not a perfect linear relationship though, but close'ish) The lower the Rs-int of a given batt, the less drop will have occurred at a given load during cranking when Rs-ext (whatever that might be) remains constant for both cases, thus more power at the starter for it to do work with.

Also, age and temp come into play with Rs-int.....So, for example as two identical batteries age and/or heat differently, each may show differing voltage drops and thus differing power delivered at the starter as well.

http://batteryuniversity.com/learn/a...and_resistance