What does CCA and Ah in battery mean

Cold-cranking amps (CCA)

It is a battery rating system that defines the battery's ability to start an engine in cold conditions.

What does a 400 CCA battery mean?

It means a battery rated 400 cca will give 400 amps of power for 30 seconds at 0 deg cel maintaining a voltage of 1.2v per cell or 7.2v for a 12v battery

And  battery rated 200 CCA will give 200 amps of power for 30 sec at 0 deg celsius, maintaining a voltage of 1.2v per cell

How much CCA do I need?

The thumb rule is one amp per cubic inch of engine displacement.

Why do batteries deteriorate at cold temp?

At cold temperatures, the reaction in the battery slows down impacting its ability to start the I.C. engine.

LO viscosity increase at lower temp making it harder to pump oil and start the engine. This makes a situation where your battery has to work harder to start the engine.

It is always better to have a higher CCA-rating battery for marine applications.

Ah rating?

Ah typically measures batteries' total energy-storing capacity.

A 100 Ah battery is capable to deliver10 amp for 10 hrs before the voltage drops to a standard value of 1.67 volts per cell or 10.02 volts for a 12v battery.

Similarly, 50Ah would supply 5 amps for 10 hrs

Ah = Amps x hours

Amps hour(Ah)= Current(I) x Discharge time (T)

CCA VS Ah

CCA is the ability of the battery to deliver a burst of power over a short time like a sprinter

Application- ➡Starting lifeboat engine, Emergency generator, etc.

Ah is the ability to deliver power over a length of time like a marathon runner. 

Application➡GMDSS battery, general service battery, etc (deep cycle application)