I am thinking about getting a small boat with a trolling motor, but I live in a high-rise apartment so I can't keep the boat at home.    I'll have to store it, and that means I'll have to take the batteries out and charge them between trips, instead of plugging in the onboard charger like I could if I had a house with a driveway.  So my question:    is it safe to charge 12-V marine batteries indoors?  My apartment has pretty good air flow if I open the living room and bedroom windows.

Yes, it's safe. I keep my boat batteries stored and on a trickle charger indoors. In my basement. Make sure the battery isn't sitting on concrete. It will drain and weaken the battery

Check your duplicate post in "ask a fisherman"

BOOM! 

I have no problems; unlike trickling setting i use deep cycle setting for my marine battery

Yes its safe, so long as the battery isn't leaking, and you don't charge it near any flammable items. Personally, i wouldn't keep it on a trickle charge anyway as its a waste of electricity and doesn't help the battery life/charge if the battery is never being discharged. Just throw it on a slow charge the day before you go fishing and it should be good to go in about 6-8 hrs.

Any lead/acid battery will self discharge while being stored and storing a discharged battery will cause it to sulfate. Once this happens the battery is junk. A discharged battery is also subject to freezing if it is stored in an unheated area. The best way to store a battery is in a cool dry place hooked up to a maintainence charger. This is a low output (1/4 amp or so) charger that can be left on continuously. Another option is to hook up a trickle charger plugged into a timer so that it runs about an hour or two per battery per day. If your battery is not sealed it is also a good idea to check the electrolyte level monthly and add distilled water as required.

Yes any lead/acid battery will self discharge, which is why I don't use them or recommend them, unless its all you can afford. If you use an AGM or Gel, it takes 12 months for it to "self discharge" to 80%. In which time if you haven't charged it to go fishing, why are you buying a boat Also, for posters reference, the comment about setting it in the basement I suppose would assume that you had concrete floors (or in a garage), however the old myth about not storing batteries on concrete floors is just that - a myth. This story has been around for 100 years, and originated back when battery cases were made up of wood and asphalt. The acid would leak from them, and form a slow-discharging circuit through the now acid-soaked and conductive floor.

AGM and Gel batteries are definitely superior, but for an occasional user the cost is probably prohibitive. I cannot justify a $300 Optima when I might use it 1 day a month at most and a $80 wet cell will serve just fine.

I suppose this falls under the half full/half empty category. Falling back to using it one day a month at most, it would beg to argue the purpose of even having a boat (in the case of the poster, having to pay storage fees, insurance, etc). I personally shop at amazon.com where I am a gold member, so i pay no shipping. They have Optima Marine batteries for $220, so to me, I couldn't justify spending $80 every 2-3 years plus the hassle and electricity of keeping it charged in the meantime, opposed to paying $220 for something that I can charge the day before I need to use it and having to replace every 5-8 years. I respectfully agree to disagree on the batteries Tom, but I believe we've answered the posters question that "Yes, it is safe to charge indoors". Tight Lines

Thanks everyone for all your input. I went ahead and got the boat and couple lead-acid batteries. It's been less hassle than I thought it would be hauling them back and forth from the boat to the apartment. A small grocery cart works just right to get them out to the elevator and down to the garage.

A good point on the Optimas. I would consider them if I owned a boat! I normally rent a boat when I need one and own a nice transom mount trolling motor that I use. Also, I rarely need to purchase a battery as a neighbor has a battery sump pump in his home and changes his deepcycle every year. He swaps me his year old and trades in the two year old that I have been using. Considering my unusual circumstance, any price for a battery is more than I am paying now!

Sounds like a pretty good deal on your behalf Tom! Jobu88, as Tom stated earlier, when you are not using your batteries be sure to check the electrolyte levels if they're not sealed. Also, don't know the configuration of your hookup, but assuming the batteries are being exclusively used for trolling motors and not hooked into a recharger on the boat, you should check into some designs on daisy chaining them (in marine boxes), local stereo shops often have relatively priced heavy gauge wire and terminal clamps that should connect well. On my 8" Coleman mini pontoon, I use a similar setup, as well as installing a cheap electric multimeter wired in so I know when I'm getting closed to drained after a long day on a big pond.