I finally got my Maxi 95 on the water this year after what has felt like half my life doing the rebuild, conversion to JR and electric drive. She has not had much use - it was already July before I got the rig set up and ready to go, but I can comment a little on the electric drive for this thread, after about ten day sails.
For background, the boat has a 10KW sailboat kit from Thunderstruck. The battery pack is 4x100AH AGM batteries, over ten years old, but I did not want to buy new batteries until I had tested everything else. The boat is kept in a marina with 220v power and I use a Victron charger/inverter (20amps) for charging. Solar is among this winter's projects, but that is OK, as I have only been day sailing as I get to know the boat this year.
In summary, the system works as it should. I have plenty of power for manoeuvring a five ton boat around the marina or in and out of rocky island tying-up spots. It is blissfully quiet, and there is no smell of diesel aboard, nor do I have to face the challenges of servicing a diesel engine without double jointed arms and elbows.
However, range anxiety - even for day-sailing - is a very real phenomenon. If I just use the motor for going in and out of the marina on a light-wind day sail, I can use as little as five percent of its capacity, which is fine. If we motor a bit further into more spacious water, or the wind is stronger, it is usually ten percent. If, as my children like, we then sail to one if Norway's hundreds of islands and stop to explore, that is doubled, or more than doubled if we have to do a bit of circling and trying different spots. Things are improving as I get to know the system. Low speeds certainly helps and at 2.5 knots in light winds, I am only pulling 8 amps at 48v, giving me a theoretical range of 12nm to 50% DoD, or about 7nm if you take out the 20% used at the marina and lunch stop. Replacing the battery pack will solve some of my anxiety here, of course, but to get up to a semi-decent range will be very expensive. At 20 amps in light winds and flat seas, we make about 4 knots, which is a more reasonable speed but, even with a lithium bank at 5KW hours (100AH ish) that will only give 12-15nm range with a bit in reserve for the mooring etc. I would rather have double that so that I am able to take longer weekend trips next year and know that I will be able to get home in time for work! I own a 1600W inverter generator from Kipor and the idea was that this would be a power supply for light wind sailing. Unfortunately, I have not been able to persuade the Victron charger to recognise an input from the generator so far. Apparently, this is a known problem with the Victron Multiplus system. There is a work around, which I will be trying when I get some spare time.
The battery pack is the big expense. In an ideal world, I would have a 12-14kwh pack, made for the boat from LifePO4 cells. At Norwegian prices, this would come in close to 25000 euros. I could make it myself from Alibaba cells for about half the price (as Arne mentioned somewhere, 48v is the limit for DIY in Norway), but I am honestly not comfortable putting together such a potential firebomb without professional help. I can use 12 or 24v batteries in series (some of them - not all - have a BMS set up for series use) but they need to have a big BMS that will take the 200 amp draw at full throttle. Here in Norway, the cost of that is a bit more palatable at around 8000 Euro for a 10kwh (4x200ah). There are other options, but these are the best two so far. The cheapest, around here, would be to buy an 8kwh pack made with used car cells at around 2500Euros. But I would have to lie about the purpose of the purchase as the CE approval specifically says that used car packs shall not be used on boats due to increased fire risks. The local guy who makes them fitted packs into boats before the rules changed, but I sail with my children, so cannot really live with taking that risk.
The regen feature on the Thunderstruck setup starts to work at about 5.5 knots, but it only cycles in and out - I have never seen a constant input into the battery pack. To all intents and purposes, I am fairly sure it does not add any more juice into the batteries than the amount of power taken by having the ignition switched to on when sailing.
As Graeme mentioned, though, motorsailing in light airs is a definite winner. The Maxi has poor steerage at very low speeds, particularly if there is a slop, and on a recent trip when the wind dropped, adding three amps of power kept the speed high enough to keep us moving in the right direction, and prevented a family mutiny from down below, where the chess pieces were falling off the board. This was in winds that were well below five knots. I am fortunate that the Maxi sails well, even in lighter winds. I think an electric drive would be a poor choice for a more staid and steady boat.
Overall, I am happy with the system in most ways, but the cost of putting a decent battery pack and solar system is going to be similar (even with the cheaper option) to the price of a brand new diesel engine. So while I am happy with the motor, love the quiet and the flexibility of it, I am not, in all honesty, sure I would make the same choice again, particularly for family sailing around the islands in Norway.