How often to charge battery

[Cheli]

This may be a silly question but I'm going to ask anyway. 

So I just read Bob's article on "Cheap & Easy Ways to Get Electricity" and I am ecstatic to find that I can have electric so easily until I'm able to get a solar system set up.

I understand I can get a marine battery and just keep it on the passenger floor and charge it with the van battery.  Then I can simply hook up an inverter (after unhooking it from van battery) and then plug in 110 or 12v accessories to charge.

So this is a two part question.

1)  Bob recommended a Cobra 400 watt inverter.  Is that powerful enough for most things or will I need to get a bigger inverter like 2k or 3k watts once I set up a solar power system?  I guess that question doesn't matter too much since it's so cheap but thought I'd ask.  I'm thinking the answer is going to be it depends on what I plan on needing power for.  Ok, so ignore that silly question......I take it back.  hahaha

2)  How long will a charged marine battery last before I need to charge it again.  I know there probably isn't an exact answer but I'm more wondering like can I get a couple of hours charging my laptop or phone before I'd have to charge it again?  As in I'll be under my hood every time I drive to charge it or could it last all week?

Even though I'm not on the road yet I'm thinking this is something I could get now and play with to get used to it and maybe even do a weekend trial in my car.

 

[phillipaaron]

1. The size of the inverter will depend on your power needs at any one time. What do you plan on using? Each electronic device must list its power consumption which you can use to add up all the totals for a good estimate. I would start with making a list of each electrical item, it's power consumption, and how many hours a day you attend to use it. From there you can do the math on how long your battery will last.

2. This is dependent on the size or Amp Hours (AH) of the battery you purchase. Once you complete step #1 you're in a better position to know what size battery you need to last X amount of time.

I'd be happy to help you out with the calculations on everything if you can get me the list I describe in #1.

 

[cherterr]

Lurking.. lol
I used this: http://www.doityourselfrv.com/bring-van-camper-life-add-batteries-solenoid-stealth-rv/
(and for OP, I think @ end he mentions some Basic ideas on what you can run).  I'm kinda thinkin' I may have more than I need?

 

[DannyB1954]

A battery does not like being left dead for any amount of time. It is best to charge them back up every day. If you take 50% out of a battery and leave it that way for any amount of time it will greatly reduce the life of the battery. As a rule of thumb, a fully charged lead acid battery that has been at rest for a while will read 12.8 volts, (right after charging it might read 13.8 volts). When 1/4 of it's charge is used up it will read 12.6 volts. At 1/2 charge it will read 12.4 volts. Accurate voltmeters are cheap these days, so I would get one, or some type of led battery monitor.

There are several ways to charge that battery. You can use the vehicle's alternator, use solar panels, or run a small generator. If you set up a heavy charging circuit between the vehicle and the house battery, you will also be able to use a large inverter for when you want to use a microwave or hair dryer, or other heavy load. You will just have to start the vehicle while you use the item.

Here are the parts that I used to link the two batteries. One relay http://www.ebay.com/itm/401111987343?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT
Two fuse holders http://www.amazon.com/Bussmann-HHX-...&redirect=true&ref_=oh_aui_detailpage_o00_s00 (one at each battery to protect against direct shorts).
Two fuses http://www.amazon.com/Bussmann-MAX6...xgy_263_2?ie=UTF8&refRID=0MXH2D4THNX80XPQPCE7
Wire capable of carrying 60 amps,(to connect the batteries). Small gauge wire, (to activate the relay).
Other components would work as well, but that is what I used. When the vehicle is started power goes to close the relay. This connects the two batteries. once the vehicle is shut off the relay loses power and disconnects the two batteries.