Boon docking, charge extra marine battery

[Dreamsongs]

Hello all!

Going to Fisher man's island state park in Michigan.

No power or hookups.

Have generator, which I can run during the day time.

Have extra marine battery and inverter to power my cpap machine (sleep apnea).

Should I charge both the camper battery and extra battery by connecting my extra battery with jumper cables to the camper battery while the generator is plugged into the RV's shore power (letting the RV's charger take care of both batteries at the same time)?

Should I hook battery direct to DC out on generator? I will not know how long to charger battery this way.

Or should I bring a separate battery charger so I know when the battery is topped off?

Thanks! I'm leaving in the morning!

Dave

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[Festus2]

Originally Posted by Dreamsongs

Should I charge both the camper battery and extra battery by connecting my extra battery with jumper cables to the camper battery while the generator is plugged into the RV's shore power (letting the RV's charger take care of both batteries at the same time)?

Should I hook battery direct to DC out on generator? I will not know how long to charger battery this way.



Dave

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Dave -

You can charge both 12v batteries (the RV battery plus the extra one) at the same time by hooking them up in parallel and using the RV converter.

Or You can use the generator in the same way. Just make sure you have the two batteries connected in parallel and use the 12 DC charging option of the generator.

I wouldn't bother taking separate battery charger along.

[Dreamsongs]

Thanks! Much appreciated!

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[Dreamsongs]

Well, I got worried about charging two different batteries with different charge levels at the same time (in parallel) off of my camper charger.

Should I be concerned about that?

I ended up charging the extra battery from the DC out on the generator. Problem is I don't know when it is charged, and I don't want to cook it. I charged it for two hours this morning. It had 12 volts before and after charging. It did not get hot.

Any suggestions?

Thanks!

Dave

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[Festus2]

Folks who have 2 12v batteries (wired in parallel) charge them up at the same time all the time using the RV's converter's charging system. I have 2 6v (in series) and charge them up as one using the converter, or our solar panels, or the generator.

As long as you have the batteries wired properly, there should not be any reason for concern.

Charging a battery on a generator's DC charging output for 2 hours certainly isn't going to fry the battery. Just make sure that, if the battery has removable caps, that you remove them while charging - otherwise you will be okay.

[Dreamsongs]

Thanks Festus!

My concern was that each battery has a different charge and each battery has a different Amperage capacity.

I used my auxiliary battery all night running a small fan and my cpap machine (with the converter). I suspect it it was pretty well depleted.

The camper battery (a huge battery, do not know amperage offhand) did not see very much use.

Is it still okay to charge both in parallel?

Thanks again!

Dave


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[Festus2]

I think in your case it might be better if you were to charge up the battery that you use for the cpap machine by itself. That way, you will know that it is receiving a charge without worrying about the other battery and what effect it might have on the charging process.

Ideally, it is better if, when charging two batteries wired in parallel at the same time, that they be the same type and the same size. Since you do have two different batteries, charging them at the same time may not be as effective.

If they were the same size and type, I would have no hesitation in saying that you could charge them at the same time.

Putting a tester across the terminals to see if you have a full charge won't give you a very accurate reading of the battery's charge condition. While it may indicate 12+volts, there is a "surface charge/voltage" that could give you a false reading. The battery should be tested under a load to give you a true picture of its condition.

[Dreamsongs]

Thanks again!

I thought the batteries should be the same when charging in parallel!

Thank you!

Dave

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[floatflyer]

I would think you could figure out the wattage draw of the c-pap and calculate from there. Mine requires 5 amps at 12 volts. 10 hours at 5 amps is 50 amp hours, or 50% of a 100 amp hour battery. But using an inverter and the 120 volt transformer will require more. If yours has a 12 volt input requirement you night look into finding our making an adapter to power it right from the battery.

[floatflyer]

Sorry for the typos

[floatflyer]

I found some info on 12 volt converters at cpapsupplyusa.com. May have to look into that myself.

[Dreamsongs]

Thanks floatflyer!

I'll look into that!

Dave

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