2 BATTERIES CLASS 27 CLASS 24?

[dick auge]

I have 2 batteries and a battery selector(1,2,all,off). Can I hook up a starting battery and a deep cell class 27 battery?

[john61ct]

So much required background info is missing there, impossible to answer.

Does the switch work for loads or charge source?

Have you got a VSR/ACR in the picture?

What brand and model batteries, or have you not yet purchased?

Adding or replacing batts?

____
Likely to be important:

What charge sources are used, how much time on shore power vs cruising or living on the hook?

Do you have a genny, run it often?

What about your Alt setup, and do you motor a lot?

[Sailmonkey]

The simple answer is yes. A group 24 and a group 27 are both nominal 12 volt batteries.
How you manage the power between them is up to you and can be as simple or as complicated as you want to make it.

[skipmac]

Short answer yes, but questions. All the questions are assuming you don't have any sort of automatic battery combiner and the wiring is otherwise compatible.

1. Are all batteries the same type, that is are they all FLA (flooded lead acid, your standard liquid filled battery with removable caps on top) or all Gel Cell or all AGM? If they are all the same then probably yes.

2. Are the batteries both more or less the same age and/or the same condition. If yes to 1 and 2 then almost certainly yes.

3. When you say deep cell I assume you mean deep cycle battery that not a starting battery but designed for heavier use and more discharge before recharging. NOTE!!! It is 99% certain that a group 27 battery is NOT a true deep cycle battery. Many are sold labeled as deep cycle or marine or heavy duty or in the UK leisure batteries. These are not deep cycle. They are at best slightly just a slightly better grade starting battery.

[dick auge]

Just trying to find a way for 1 battery to have more cranking power and the other 1 to use as a deep cycleg

[Cheechako]

Yes you can.

[Sailmonkey]

Originally Posted by dick auge

Just trying to find a way for 1 battery to have more cranking power and the other 1 to use as a deep cycleg

You may be better served by a pair of gc2 golf cart batteries instead of a group 31 battery.

[john61ct]

Any good decent sized true deep cycling batt will handle the Starting duties no worries.

Very few auto-sized 12V like G-27 are true deep cycling, and they're not sold in big box or auto channels.

For a small setup if you have space and budget, I'd recommend going for matched sets.

​The best battery value by far is Duracell (actually Deka/East Penn) FLA deep cycle golf cart batteries, 2x6V, around $200 per 200+AH pair from BatteriesPlus or Sam's Club.

Two pair of those will give great reserve capacity (400+AH), flexibility and redundancy.

If you want sealed and or 12V, then G31 Odyssey PC-2150M is a great choice, maybe two paralleled for the House bank and one on the Starting side.

[john61ct]

The 1/2/B switch should be used for switching loads, not charge sources.

Problem is left on Both by mistake you're dead in the water.

ACR/VSR will automate the isolating, better solution. Also allow all batts to be charge by any source from either side.

[captstu]

I think your best deal for the money and space is to get 2 Group 27 (or similar) batteries from Walmart for about $80 each with core exchange. Place them in 1 and 2 and leave the switch in Both. With the money you save, buy a "dead start" battery - about $80 and keep it in a locker dry and out of the way. If you forget or something goes dead, use the small clip on battery to start the engine and try to recover. This is the safest way to be sure you get home with the least cost and risk.

[Cheechako]

One thing I've found about "dead start" jumper batteries. You better charge them often or they dont retain enough to start an engine. I bought a highly rated one too.

[john61ct]

The bigger sizes of lithium jumpstarter powerpacks can start even a large diesel, and can be topped up every 4-6 months without losing much charge, much better than lead, slip into a jacket pocket, can be used to recharge a phone or computer.

Walmart doesn't sell any true deep cycle batts afaik, only ones fraudulently labeled as such. Same with all automotive or big box sources.

The Deka / Duracell 6V GCs spec'd above are a rare exception.

[waterman46]

Originally Posted by dick auge

Just trying to find a way for 1 battery to have more cranking power and the other 1 to use as a deep cycleg

Seems you are asking two questions. Most folks will have a high cranking power battery for engine starting and in your case you could use the group 24 smaller one for that. Then ideally you'll have a deep cycle battery in a larger size for house battery. As some have commented, you may not be able to find a true deep cycle in Group 24 size, so see if you have room for a 4D. If not, the Group 27 will be acceptable for a smaller boat with few high consumption devices.

NO problem as long as neither is gel cell (AGM and FLA are compatible) and both batteries are close to the same age and usage condition. Without seeing your 12V schematic, we can make only a few general statements beyond this.

Feed all charging sources (shore power charger, solar and alternator) in parallel to the batteries. Probably best to connect the voltage sense wires from the charging to the house battery as it is the one that will be most active.

People may tell you that parallel charging will overcharge one of the batteries but this is not true again as long as both battery chemistries and age/condition are close. The total charging current will be divided in proportion to the charge state of each battery.

IMHO all batteries should have a main disconnect switch on their + terminal circuit. But be sure the engine isn't running if you switch both off as that could fry alternator diodes.

Unless you manually switch battery charging and output from one battery to the other, you need to have some kind of battery isolator. If you use a diode battery isolator make sure both batteries are being charged through the diodes in that isolator so the voltage drops from the charging source will be identical to each battery. Or use something like the echo charger running to your starting battery. There are also voltage controlled relay types; its an older technology that reduces voltage drop but my experience is that the relay contacts burn out over time and go resistive.