From: paul dove <>
> Current out of a battery is not calculated based on internal resistance.

Actually, it is. The Equivalent Series Resistance (ESR) of a battery is not a 
theoretical number. It is found empirically by measuring the voltage drop 
caused by a high-current load. The voltage of a 6v golf cart battery really 
does drop by about 2.5 volts with a 500 amp load. In other words, it acts like 
an ideal 6v battery with a 0.005 ohm resistor in series. Thus, it's a 
reasonable way to estimate what you are likely to get.

> you won't get 100% efficiency out a controller.

No, of course not. But the efficiency is pretty high, and can usually be 
ignored for back-of-the-envelope estimates. That's all I was trying to do with 
my estimate.

>The battery industry uses a 100-hour rate as an index to compare batteries of 
>different types and sizes.

They do when they are trying to exaggerate the capacity of their battery. For 
EV use, the 100-hour rate is useless. Even the more common 20-hour rate is 
nowhere near the rate at which the battery will be used. What you want to look 
at is the 1-hour or Reserve Capacity rates, which are what you will get when 
discharged at high currents. For a golf cart battery, the reserve capacity is 
measured at 75 amps, and the 1-hour rate at about 100 amps.

But, I don't think these capacity numbers are what is limiting the maximum 
current in this case. My guess is that these golf cart batteries can only 
deliver 200a before their voltage sags to 72v and the controller starts 
limiting current.

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