On Mr. Wiggles, my 1976 CAL 2-27, I have a Motenergy 5kw BLDC motor and a Kelly controller, 2:1 Baldor gearbox, and until a couple days ago had the original (too small) 2 blade folding sailboat prop, just replaced with a 14"x10" 3 blade that was given to me. Battery bank is 8 6v GC-2 golf cart batteries from Sams club, at $85/ea, about 220ah, in series for 48v. You can indeed increase battery life with a battery management system, assuming you can find one designed for 6v batteries. However, like a lot of things that would be great to have, I simply cannot afford that. I would rather go ahead and replace the batteries every 5 years or whatever, for another $680. However, careful battery maintenance is important. I have a single installed 4 bank 12v charger with isolated outputs and each output charges two batteries. I also built a fully manual charger for equalizing, etc, using a variac and a rectifier from an arc welder, and I can charge 6v batteries individually, or the whole bank at once with that. Such a system must be used knowledgeably and attentively. Manual charging must be done correctly and monitored carefully! The manual charger I use only for equalizing and as a backup to the automatic. Batteries bought together, from the same month, will usually charge and discharge fairly well together in series, at least for the first few years. Careful testing in the initial 30 hours or so of operation is important to weed out any possible bad batts. Keep them properly filled with good water, free of minerals. I use distilled water and that is what I recommend. It is simply too cheap to not use it and have several gallons on hand. Ideally you would log water added to each cell, and specific gravity at rest. Okay, all this is a PITA but important for optimum battery life. Oh, and a handheld IR thermometer is a very nice thing to have, inexpensive, and a bit better than just feeling the batteries. Not saying going without BMS is a good idea, but it certainly CAN be done if you don't mind a little extra work and attention on your bank, if you are like me and operating on a working man's wages that are already spent on other stuff.
FWIW I do not know anyone with 6v or 12v flooded cell lead/acid batteries who uses a BMS.
As for splitting up your bank, the 50" run of wire to the outlying batteries is definitely a problem unless you use nice heavy cable. I use 2/0 welding cable because I was able to source it cheaply and it is very flexible and easy to handle. This size cable might look awfully big but I think a bit of overkill here is a good thing. As another poster mentioned, keeping + and - cables bundled together is a good idea especially if they pass within a few feet of a compass. You can't adjust your compass to compensate because the current in the cable does not stay constant.
If you will be charging or discharging with the boat heeled over or rolling, it is essential that flooded cell batteries be oriented in the proper direction to avoid the top corners of the plates being uncovered. Generally they should be pointing p/s and not foreward/aft. Remember, it is the shape of the individual cells that matters. The electrolyte in the cell does not care what the overall shape of the battery is like. This may impact your placement scheme.
Remember also that you are replacing a 250 lb engine and fuel tank with a considerably heavier weight of batteries. It is convenient to tuck them up in the engine room, but remember FWIW you are adding weight well astern of the keel. Also out of sight, out of mind. Don't neglect your battery maintenance due to difficulty in accessing the batteries. Me, I installed my bank in the cabin, just aft of the keel, and the battery cover is a seat and also the companionway step. One big step instead of 2 normal ones. Works okay, cause I have pretty good headroom. Eventually I will install a second bank in the space just aft of the vee berth, where the head and vanity are located now. The new head is already in place in my shower cubicle which I built a couple years ago... the only one I know of on a Cal 2-27.
I am liking the setup just fine, so far, and it has proven to be a very good replacement for the old atomic.
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