There has been a bit of chat in regards to the 4V charge limit on the thundersky batteries - a lot of people reckon its pointless, as the surface charge burns off very fast - its an upper limit, not a recommendation. Some crappy BMS'es will allow the voltage to get that high.
Of course it is totally pointless and probably a lot better to stop at 3,6 volt like regular LiFePo4, from 3,6 up to 4 volt is maybe 5 wh energy more and you burn that off in the first meters of your ride, but that's why I charge them only up to 14,2 / 4 cells is 3,6 volt per internal cell.
When I just had my cells for a few months, I went for a ride but got lost ( just moved to another area ) and my ride was longer then planned, Actually I drained 20,8 Ah out of the blocks
but still no performance loss, huge sag or anything....probably very close to the famous lithium knee but not there yet, so they are a bit underrated also, never happened again, stupid mistake on my part and luckily they charged up like fresh cells.
About the voltage sag, when I pull 2000 watt for longer periods like 5 minutes on a long incline, voltage will sag about 7 volts from a 50% charged pack, that is for 4 blocks in series from 53-ish volt to 46-ish volt, amp draw little over 40+.
I can try to see what the sag will be at 400 watt for you when you want, I can regulate the output via speedict and take for a spin if interested and post the outcome for you.
Most important especially with these unregulated 12 volt blocks is to leave some safety charge in them I think, only drain them for 80 - 90 % max. of their rated capacity, the internal cells will become unbalanced if drained to much too often and that will likely kill these and there is no BMS to regulate that, just with any lithium cell of whatever chemisty, balancing is ( almost ) not needed when you leave some energy in it.... drain is pain.
On the other hand, lead starts degrading the moment you put a load on it and, capacity wise, becomes worse and worse every time you drain them even to 50 % state of charge, if you leave it for a couple of days like that a noticable loss in capacity will be your part, and before you know it you are carrying dead weight on you boat. ( 3 years at most ) I know this first hand because my uncle also has a lead acid powered canoe and has to change the battery every few years, told him to get lithium, but high initial price puts him off.
This summer I bring my thunderskies and he can bring his 2 leadies, one 60 ah and one 80 ah, take 2 of his canoes and have a showdown haha, I know the outcome hands down, my 80 Ah will crush his 140Ah..... my canoe will plane
Oh one other thing, when storing almost every lithium battery for a longer time, charge it between 50 and 75 % , not full not empty and keep them cool, they live longer that way.
Oh one other other thing, a cheap celllog ( hobbyking / dealextreme ) can monitor your voltage and can be set to scream @ you when your voltage gets critical, Turnigy watt meter is also very handy ( hobbyking ) to see what you have drained from the battery, both very cheap < 40 dollar total.
I'm from Belgium BTW.
