Add a 3rd battery?

[brain_rinse]

I have space by the current 2 battery setup to add a 3rd. Is this a viable option? Does it increase the amount of stereo float time we'd have significantly? Appreciate any input.

[David Analog]

Sure, increasing the collective battery(s) reserve time (in Amp/Hours) will increase your float time.
There are two key measurements that will determine what your needs are.
The voltage level after a long duration at rest. The lowest depletion level for a deep cycle battery should be no lower than 11.8 volts. If you ever go lower you need more battery capacity.
The second is the voltage after your return once all charging voltage has fully dissipated. A fully charged new battery should be 12.7 to 12.8 volts depending on the chemistry. A bit lower with age and use. It’s unlikely you’ll burn enough gas for full restoration after a long float.
More battery capacity will definitely increase your dependency on AC shore charging. More capacity that cannot be fully restored is a liability rather than an asset.
Keep in mind that most modest chargers are only built to handle one large battery per bank so charger capacity has to match your unique combination of a) total Amp/Hour capacity, times b) normal depth of depletion.
It’s recommended that the two batteries in parallel on the house/stereo bank are of the same chemistry, age and usage level. It makes mixing in a new battery with an aged battery a concern. However, if all else is equal you can parallel two batteries of different Amp/Hour capacity.
I know I’ve abruptly thrown a lot your way. I’ll clarify any point as needed.

[brain_rinse]

That helps a lot - thank you. I am OK needing to put a charger on the batteries after a long day on the lake, and do have a new charger. Based on what you've said I'm going to research the true abilities of the charger to make sure it's up for the task, and I'll also check the voltage of the batteries I have.

A little more info: I have 4 matching batteries. 2 are old (and currently installed in the boat) and 2 are less than a year old (and sitting on a shelf.)

So can it really be as simple as hooking up that 3rd battery in parallel to the current stereo battery? No switch or ASR changes needed? This is sounding like it could be a very easy upgrade.

[MLA]

It is as simple as wiring the 2nd battery in parallel to the existing house battery. Its always best when the batteries are the same age. What about using the 2 existing batteries as the house bank and then drop in one of the batteries off the shelf as the main cranking? Or use the 2 unused batteries off the shelf as the house bank and pull one of the existing.

[brain_rinse]

It is as simple as wiring the 2nd battery in parallel to the existing house battery. Its always best when the batteries are the same age. What about using the 2 existing batteries as the house bank and then drop in one of the batteries off the shelf as the main cranking? Or use the 2 unused batteries off the shelf as the house bank and pull one of the existing.
I could do either, whatever would be best. I know it would be ideal to have all be the same age, but I want to use up what I've already got. Realistically I don't think the older batteries will last much past this season.

[David Analog]

Just that simple.
I guess it's not such a big worry over battery degradation caused by different battery efficiencies when you are going to upgrade in the very near future.
But don't stretch the life of batteries too far past their time, as it can be particularly hard on the alternator.

[brain_rinse]

But don't stretch the life of batteries too far past their time, as it can be particularly hard on the alternator.
I hadn't considered that. Maybe I'll have both the old ones tested before throwing the 3rd into the mix.

[viking]

Because you have the 12v batteries already and sounds like a 3bank charger then sounds pretty easy and I'd use your newer 2 for the house side. If you didn't already have the batts I might suggest a couple 6v.

I have a question for the experts regarding an existing setup.
- 2 new 12v batts with existing Powermania TurboM212v2 on board charger.

I plan on monitoring the voltage of the house batt during the upcoming season but I'm not very optimistic about playtime with the new stereo system. I can't add a 3rd batt without needing to purchase a new 3 bank charger as I don't believe my Powermania model will work?
Because I have 2 fairly new 6v I'm considering using those wired in series in place of the single 12v house batt and inquiring as to compatability with and be able to use existing charger and extend my playtime with the added amp hours? Will the charger work with the six volt setup?


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