battery charger tender

[mikefree]

I am starting my electrical portion of my build and am not sure what to buy to keep my 12v battery alive. I am not running much 12v. Led lights, 2 computer case fans and a phone charger or 2. perhaps a car radio. I am planning on running shore power to a power bar with an overload fuse on it. From that Ill run my 110 stuff and my battery charger. I was first looking at the battery tender plus but then for a few bucks more i saw the genius 3500 and it seems to have allot more bells and whistles. I will be mainly camping with power hook ups but im sure i will go a few days now and then with out a plug in opportunity. I read that the maintainers will not charge a battery that is out of juice but instead just keep good batteries good. I used allot of technical words there i know.
Long and the short of it does this mean ill have to pack an actual charger as well?

[MtnDon]

What you need for a charger depends on what you have for a battery, specifically what the amp-hour capacity is. Ideally a battery would be charged at no more than C/10, where C= the amp-hours of the battery. For illustration let's assume you have a fairly typical 12 volt RV/Marine battery, like an Interstate SC31DM; 75 amp-hours. Divide the 75 by 10 = 7.5 amps. A 7.5 to 10 amp charger would be better than the Genius 3500.

If the AC power source is grid power the genius3500 would charge the battery. Eventually. Depending on how depleted the battery is that could take the 3500 longer than an overnight stay in a campground.

Note on batteries. Flooded lead acid batteries should be recharged within a day or so when their charge is depleted down to 75% or less remaining capacity. A low powered charger may take days to rebuild the charge to full. That is not best for battery longevity. That said many RV batteries are abused; it simply means premature replacement.

Also note that a battery charger rated at xx amps will not charge the battery at xx amps for the entire charge period. The amps into the battery tapers off as the battery gets fuller and fuller. The last 20% of the charge takes longer than the first 80%.

So yes, you should have a good battery charger along. One reason many TD builders use something like a PD4045 is that is contains an ideal battery charger and maintainer as well as all the circuits and fuses needed for both AC and DC. The power may be overkill for many TD's but it is a very effective unit.

[mikefree]

Thanks for the info. The more i build on this the more i see its hard to do allot on the cheap.