I have a champion Battery that says it has 530 amps (cold crank) and 730 amps (cranking). Is this normal for a car battery? I only ask because I was reading some alternater discussion and someone said it takes like 70 amps to crank the engine. I just want to know if my battery is a good brand and at what point I should consider replacing the battery.

Thanks
-Max

 

That's sufficient for a 7 as long as no "heavy" electrical add ons. Replace when battery gets weak.
FYI-I have a Sears Die Hard that's been in my '89TII since 1994. Going on 10 years and no problems yet!

 

The rotary engine is one of the easiest to crank.
Torque is no problem, only speed if your compression is low.
A lawn tractor battery will work in an emergency.
Accessory loads are the main issue.

 

Thanks for the input. I don't have any electrical mods or even a good stereo.

-Max

 

Using a clamp on DC ammeter, I have measured starting currents of 300A or more for a few seconds when starting a cold issue. 70A is only 0.1 HP, and starter motors are rated at usually 2HP (1400W, or roughly 120A at 12V) and are normally about 50% efficient. Many smaller batteries will dish out this kind of current (I have some 4.5A AGM 12V batteries that are rated for 250A surge), but the amount of time during which they can do that is minimal. Since RX-7s like to flood, it's nice to have a battery with a large AH capacity for extended cranking periods. I believe the Optima Red Tops are rated at around 50 AH.

Of course, no one ever reads battery capacity in AH when talking about cars. They always talk about CCA, or cold cranking amps...Anything over 500 is fine.