Battery C20 or C100

[Gryphon2]

I need to replace 3 big AGM batteries which are rated as 160 Ah and C100. I have been told that I would get the same performance from a 140 Ah C20 battery. True or false?

 

[andsarkit]

Quite possibly true if you have a quick read about Peukert's law. The capacity reduces if you draw higher current.
Of more use is the number of cycles to a specified depth of discharge. This will indicate whether the battery is more biased towards low current deep discharge in a house battery or short high current low DOD in an engine start battery.
Peukert

 

[BabaYaga]

I need to replace 3 big AGM batteries which are rated as 160 Ah and C100. I have been told that I would get the same performance from a 140 Ah C20 battery. True or false?

The rating for the existing battery would be 160 Ah at C100. The C figure says nothing about the battery, it is just a qualifier of how the Ah figure was arrived at. Ah gives an indication of the energy storage capacity of the battery. Because this can be measured in different ways, for instance regarding discharge time (number of hours indicated by the C figure), this is normally stated to make comparisons between batteries easier. I believe C20 is most commonly used by manufacturers when declaring a battery's capacity.
Performance is a much wider concept, for a 'house' battery the number of expected cycles is, as mentioned above, one of the more important parameters.

 

[PaulRainbow]

I need to replace 3 big AGM batteries which are rated as 160 Ah and C100. I have been told that I would get the same performance from a 140 Ah C20 battery. True or false?

Close enough.

But, it won't be a different battery, it's just a different rate of discharge for the same battery. Your current batteries are:

160ah @ C100
148ah @ C20

That might vary a bit depending on the exact battery, but it's close enough for here. C20 is the energy a battery can deliver continuously for 20 hours at 80°F without falling below 10.5 volts. C100 is the energy a battery can deliver continuously for 100 hours at 80°F without falling below 10.5 volts.

 

[lustyd]

is the energy a battery can deliver continuously for 20 hours

Not worded quite right, although obviously your point is correct.
It's the energy the battery delivers in 20 hours. 7.4A would be what it delivers continuously for 20 hours, while 148Ah is the total delivered over that time.

 

[Gryphon2]

Thank you for the input from those more knowledgeable than I!