5.7L EFI Battery sizing

I have a 2000 rinker with a mercruiser 5.7L EFI that i bought from a first owner last summer. I had starting problems recently and have been doing a ton of troubleshooting. One of the posts here stated that the EFI controller is very sensitive to lack of charge.
The previous owner had gotten 2 new batteries with 550CCA each. I sent an email to mercruiser and they responded that the minimum CCA for my engine (V8) should be 750 to 800. The local dealer said they don't send V8's with less than 1000CCA.

i am wondering if my intermittent spark problems are as simple as too small a battery? If the battery switch is placed in the 1 and 2 (both) position does this help in starting.
I am leaning toward replacing one of the deep cycles with a cranking battery at 1000 CCA and using it just for starting. Is it ok to mix and match like that?

thanks

Re: 5.7L EFI Battery sizing

i am wondering if my intermittent spark problems are as simple as too small a battery?

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Nope, not your problem.

The reason for minimum battery size is for cranking and stating the engine without too much voltage drop that would cause the ECM to not allow spark or fuel if the voltage is below a certain level while starting.

With EFI, they recommend a starting battery, not a deep cycle. Deep cycle batteries show too much of a voltage drop while starting.

Do you have the OEM service manual for you engine? If not, head up to the Adults only sticky at the top of the forum and download it.

Re: 5.7L EFI Battery sizing

I downloaded that manual recently and it has many things that my Seloc book does not have so THANKS for that info. Both of these batteries are deep cycle that he left me. Can i get away with buying one cranking battery and leaving the other, using the crank for just starting?

Re: 5.7L EFI Battery sizing

turfguy1969 said:

I downloaded that manual recently and it has many things that my Seloc book does not have so THANKS for that info. Both of these batteries are deep cycle that he left me. Can i get away with buying one cranking battery and leaving the other, using the crank for just starting?

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Yes you can. Put your starting battery on 1, leave it there to start, then switch to both when traveling. when you get there switch to "2" to drain your deep cycle with the radio etc. Switch to 1 to start it up and travel home.

You will find starting is better with a true starting battery. Deep cycles just don't give you what you want..

Re: 5.7L EFI Battery sizing

I have a 97 5.7 EFI. I've got a starting battery and a deep cycle. No problems there!