Best boat battery chargers according to redditors

Yes I think getting the batteries to a known state is the best first step. Once they're fully charged by a decent charger you can just let them sit 24hrs and see what the voltage is then. Healthy batteries should settle down to 12.6v after being disconnected from the charger. If they go much lower, or more to the point if they continue dropping below 12.3 while they're disconnected then they're bad and probably can't be recovered.

A trickle charger won't do it though, you need something that has a setting for sla vs flooded batteries and that can drive at least 10A and you need a voltmeter and ammeter, built in is best - some way to continuously monitor the progress. If it's not a quality 3-stage charger then just watch it as the voltage rises to 14.4-14.5 and then watch for the amp draw to fall off. The rule I go by for terminating charging is 5% of the 20 hour amps capacity rating of the batteries. If those are 100AH for 20 hours rated then that's obviously 5A. When the charge current drops to 5A you're done with that one.

Note that most solar charge controllers require that the solar inputs to the controller never be active unless there's a battery connected on the battery side first. I blew up a Chinese controller this way once though not nearly as nice a one as you have there ($12 on Amazon).

Any 10A or bigger charger will work provided it can be set for sla batteries

These following units are cheaper on marine sites. Just google the model number.

A good one:

https://www.amazon.com/ProMariner-43012-ProSport-Generation-Battery/dp/B00F5EBR1C/ref=mp_s_a_1_7

A superb charger for permanent install as generator driven backup to your solar:

https://www.amazon.com/ProMariner-63170-ProNauticP-2420P-Battery/dp/B004S63NIS/ref=mp_s_a_1_4

To do specifically what you want use this:

https://www.amazon.com/MinnKota-MK-2-DC-Dual-Alternator-Charger/dp/B001PTHKJY/

That's how my trolling battery gets charged

Manual switches are bad cos they are manual and you tend to forget...

Amazon sells decent boxes for this.

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In my 93 I just ratchet strapped a square milk crate to mine and kept jumpers and chains in it mostly.

To run your AC (and everything else, although they're really negligable) that long, you're going to need 37 100w solar panels. That's probably not going to fit on your bus, and by the sounds of it, it definitely won't fit your budget. Also, that 100w rating assumes that these panels are at a 90 degree angle to the sun. So, you'll need to tilt the panels. That also assumes you don't have losses from a crappy PWM solar controller. So, you're going to need MPPT controllers, which are expensive ($550 and way up). And you'll run four 6v Trojan T-105REs down to damaging levels in just two hours.

So, you're best bet is to either use your bus' engine as a generator, in which case I suggest an alternator to battery charger (These get much more power out of your alternator than a simple isolator will. They are well worth the money.) or buying a generator tied to a charge controller (You'll want/need the charge controller if you plan on plugging in anywhere anyway). The generator is by far more efficient (quieter and smells better), but you'll have to find a place for it, and store gasoline for it. It's more expensive up front, but cheaper in the long run.

Another tip would be to get a smaller AC unit. I'm in Texas where the weather is just as hot, if not as humid, and I'm running two 6,000btu window units. That way I can run one when I need to conserve power, and two when I can plug into "shore power" at a camp site or friend's house. New window units are cheap. And running just one of those will only cost you 7kW for the day instead of the astronomical 26kW you're talking about. I think my whole central air system at home uses less than 26kw a day, and I like it COLD!

With my setup that I'm building currently, I'm going to run the alternator to battery charger for when I'm driving (free power), 4x 250W solar panels on tilting racks, a MidNite Solar Classic 200 MPPT solar controller, a 3000w inverter/charge controller combo, 8x Trojan T-105REs, and a 30A shore power plug. I expect my total setup to cost me just under $5k. I also intend to add a second set of solar panels and solar controller next year to get another 1kW of solar up to need to run the bus engine less often.

or charge with:

https://www.amazon.com/dp/B06XK7PM9F/ref=sxts_sxwds-bia_1?pf_rd_m=ATVPDKIKX0DER&pf_rd_p=d754fdf0-fd52-4edd-8917-8e65a84c20d5&pd_rd_wg=7nQKl&pf_rd_r=YS6V4J7WZ257BVW0RJ7S&pf_rd_s=desktop-sx-top-slot&pf_rd_t=301&pd_rd_i=B06XK7PM9F&pd_rd_w=zoiM2&pf_rd_i=12v+charger&pd_rd_r=3b5f51d8-6f17-4df7-a9a2-9e9a335d1413&ie=UTF8&qid=1535782504&sr=1

I've got similar electrical needs to you, currently move between inverness and the central belt and have 290w on the roof. There have a couple times where it's been dreary for a few days and the batteries have rundown near to 50%, so in those events I've limited my usage and gone for a wee drive the next day. Hasn't happened too often though.

If you're driving every day you might be fine without solar but I would look in to a proper battery charger like one of these (https://www.amazon.com/Sterling-BB1230-12-Volt-30-Amps/dp/B071DMV7PF/ref=sr_1_1?ie=UTF8&qid=1535726827&sr=8-1&keywords=sterling+bb1230). I only mention it because my 'smart' relay only pushes 14.6v in to the batteries which isn't enough for an equalize charge and they'd end up dieing prematurely if it was the only charging source.

I'll plug this fridge too as it's awesome and uses very little power.

Yeah, you'll definitely want more. However, I sort of question how much battery capacity you have to begin with. That's ALOT. What are you running?

If you could cut some capacity (and space/weight), it would allow you to top off the smaller amount easier, which is probably better for their longevity. Keeping them at a continual partial state of charge is much worse than closer to full.

I figure daily solar/alternator should be able to cover 1.5-2 days of usage, and battery capacity should cover 3-4 days usage (to make up for days when you don't drive/have sun).

And no, the issue isn't with the alternator - the limiting factor is the current that the batteries themselves can accept. The alternator is probably running at 10% output when they get to 85% SOC. I dont know the specs of the CTEK unit, but I suppose it is possible that if a device were to trick the alternator into outputting higher voltage and/or convert it to a higher voltage, then more current would flow into the batteries. I know in the marine world people get some pretty fancy (and expensive) alternator regulators that have multi-stage charging profiles which presumably give a little extra speed. But it doesnt seem like an economical choice to be honest, and surely has efficiency losses that would negate some of the benefits. I'd rather put the money towards another solar panel or two.

One device that I had looked into, but didnt end up getting because I got lithium batteries and needed a different setup, was this:

• https://www.amazon.com/Pro-Alternator-Battery-Charger-130A/dp/B008BJ44Q8/ref=pd_sbs_263_t_2?_encoding=UTF8&psc=1&refRID=3MTH581C89SS5KJPCPTB
  
• http://www.sterling-power-usa.com/SterlingPower12volt130ampalternatortobatterycharger.aspx
  
  It seems much more promising than the CTEK units that I've seen around here. It actually does what I was saying - tricking the alternator and converting voltages to optimal levels.
  
  But again, I'd just get more solar.

Have you seen this?

Sterling BB1230-12 Volt, 30 Amps - Pro Batt Ultra Battery to Battery Charger https://www.amazon.com/dp/B071DMV7PF/ref=cm_sw_r_cp_api_i_Xg9RCb3FA8T5T

Its able to charge LFP AGM etc, theres only 2 reviews and one is probably from the company, but it seems like a great solution. The issue is that its not readily set up for direct solar hookup and you need an extra MPPT charge controller for that.

I went with one of these.

Highly recommended by other dwellers and This blog has a great review on it.