House batteries

[wa8yxm]

Marine batteries are not as forgiving as true Deep Cycle batteries should you OPPS them (Very deep discharge)
For any given size battery, save for OPTIMA types, the capacity is very close to all other batteries of that size, makes no difference if starting or Deep Cycle.. What is different is how far you can run 'em down before damage sets in.. Starting, Marine and MARINE/deep cycle do not like half full thy like to be fuller that that.. DEEP CYCLE does not mind a 50% state of charge.

If you go 12 volt.. look for Trolling batteries as opposed to MARINE/deep cycle.. Trolling is a deep cycle service.

[nothermark]

Maybe. The issues is how fast you can get that power. Deep cycle batteries do not like big current loads. When you hit the switch wait a minute and the Deep cycle house batteries will load the faster starting batteries. Hit the key after a minute and then the starting battery can pick up most of the load. Chances are you do not need a lot more power than the starting battery had anyway unless you let it run really flat.

FWIW it works both ways. If you get up in the morning and the house battery is too low to start the generator you can start the main engine and give things a couple of minutes to stabilize. That will often let the genset start off the house batts plus whatever the engine alternator is feeding back to the house. If not hit the switch to connect the battery banks while hitting the generator start. That can take 2 people. ;-)

[chideock]

That's good to know about the 6volt. Like the OP I have 2 12volt (interstate) in parallel. They came with the MH which we bought used so I do not know how old the batts are. I suspect I will have to get new ones shortly, we have had the MH one year now.

The OP questions are relevant to me as well. We do not boondock either-always at CGs with power.

[ShapeShifter]

Originally Posted by dennis45

I have seen 120AH 6V flooded batteries in the range of $120 each (or less). So, two (giving you 240 AH) would cost you about 240 plus bucks.

Sorry, the math doesn't work that way. Batteries in series increase voltage, but not current capacity. Batteries in parallel increase current capacity, but not voltage.

Two 120AH 6V batteries in series give you a 120AH 12V battery.

If you think in terms of power, the math becomes a little clearer: power (Watts) is voltage (Volts) multiplied by current (Amps). Or going the other way, power divided by voltage gives current.

• A 120AH 6V battery has 720 WH (Watt-Hours) of capacity. Two would give you 1440 WH. Divide that by 12 volts: that's 120 AH. By going in series, the voltage increased, but the current capacity didn't.
• A 60AH 12V battery has 720 WH of capacity. Two would give you 1400 WH. Divide that by 12 volts: that's 120 AH. By going in parallel, the voltage stayed the same, and the current capacity increased.