Selecting Batteries for Engine Starting

[otter]

In c.2020 I purchased a 1998 OUTRAGE 17 with a Yamaha 130-HP engine. I understand the general principles and functions of an engine cranking battery and a deep-cycle battery and their functions. I don't know much about electrical rigging. I believe that having two batteries equal in power ratings on a boat is recommended.

Q1: will using one cranking battery and one deep-cycle battery cause a problem?

Q2: if the cranking battery cannot start my Yamaha 130-HP engine, will a deep-cycle battery be able to crank-over the engine and start it?

The boat has two c.2017 NAPA-brand flooded-cell deep-cycle recreational vehicle marine batteries rated 500 CCA or 615 MCA connected to a battery selector switch.

Q3: should I replace the port deep-cycle battery with a cranking battery, and replace the starboard deep-cycle battery with a new deep-cycle battery?

[jimh]

I believe that having two batteries equal in power ratings on a boat is recommended.

If you cannot pull-start the 130-HP main propulsion engine on your 1998 OUTRAGE 17 boat, then having two batteries aboard that can each on its own crank over the engine for starting is a good idea.

Q1: will using one cranking battery and one deep-cycle battery cause a problem?

There is no particular need to use a deep-cycle battery as an engine starting battery. Generally deep-cycle batteries are NOT used for engine starting.

The boat has two..flooded-cell...marine batteries...

As your outboard engine is an older model, it may not have modern voltage regulation on the charging output. With poorly regulated battery charging voltage, only flooded-cells lead-acid batteries should be used. Monitor the electrolyte level in the flooded-cell batteries to be sure that electrolyte is not being lost due to excessively-high charging voltages. A proper battery charger should only provide a well regulated 14.4 to 14.5-Volts of charging output.

Also, older outboard engines in general (particularly some Yamaha models) had very limited battery charging current output, sometimes a little a 6-Amperes. Asking an outboard with limited charging current output to re-charge a deep-cycle battery from a very deep state of discharge would not be a good idea. You could easily cause damage to the battery charging circuit of the outboard engine.

In the absence of any information about how the battery selector switch is configured and what electrical loads are in use on the boat, the need to use a deep-cycle battery, that is, the need have the ability to deeply discharge one of the two batteries on the boat on a routine basis, is unknown to me. Without that information, I cannot see a justification for use of a deep-cycle battery for engine starting or for back-up engine starting.