I did similar and accidentally left the Starlink and fridge on overnight from warm without switching on the mains charger. The fridge is cold enough to make ice, and we never set it warmer as we like ice. No problem, 70% by morning because we have lithium, so actually I could have gone home for the week and still been fine.
I think you're confusing 80% discharge with discharging to 80% SOC.
I'm not confused, and you seem to have understood me.
£369 actually, and it'll still have more usable capacity. You've picked some shitty batteries to compare a good one to, I suspect your cheap batteries will be dead in a couple of years so you'll need 8-10 of them to compare properly.
Nonsense, I invested £850 to make my time on board more comfortable and manageable, and £200 of lead doesn't achieve even close to what we have. We don't have the space or money for an equivalent lead bank, nor do I want to deal with constant degradation and low voltage alarms. Nothing shiny about it, the technology is better in every way. If you can't afford the initial outlay, or don't understand it fully then I'm sorry. You will certainly spend more in the long term than I have, and will have less capability in the mean time. I've not made a mistake, and I definitely have a better system than lead without a shadow of a doubt. That clearly triggers you and I appologise.
This is a simple 27' boat with very basic demands and poor generation used maybe 50 days a year. Like many similar boats it will be fine with between 200-250 lead acid. Apart from the small size, none of the other benefits of Lithium apply - no heavy discharge fast charge acceptance (only a puny 35A alternator and a 50W solar) and would never reach the theoretical number of life cycles to justify the cost of the installation. Intelligent use of fridge is of course important. Talk of power audits is a waste of time only if you are too lazy to do it. Nothing difficult about it and as an exercise it identifies ways of reducing power consumption so that you don't need to spend excess money on capacity you don't need.
That’s just the thing though, it no longer is more expensive per usable Ah.
Indeed, ours does take over 10 hours. Lithium doesn’t need to get to float though and we don’t need to be present while the solar charges them during the week. We’re now saving quite a few quid on shore power which we used to use to charge the lead bank. Even on long trips we get enough from solar and engine use to keep them within usable range for a month or more even if the engine is only used to heat water for 30 minutes a day and we only have 200W solar.
Where on earth is this “must be on board”to recharge la batteries coming from?
Because with the smaller capacity you must charge as you go along while on the trip to avoid permanently damaging the lead bank. Applying the same logic to lithium as for lead is the problem here, and experience is working against many contributors. With lead, it's better to leave them full and on a trickle charge while lithium is best served if it hits 99% as you step aboard for the next trip.
But I think you have it the wrong way around. Live aboards have the time to look after lead and are there to monitor them. The weekender that gets back to their mooring at 50% charge and has to leave to get to work the following morning may well have killed their lead batteries if they don’t return for two weeks or more. A small solar panel isn’t enough to rescue that lead bank but it is enough to gradually fill a lithium which will sip any tiny amps provided.
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Some boats might have to in order to not kill their batteries, but others might sail to the moorings and motor only for 5 minutes, which with Lead will not even move the dial.
The problem there is that more solar doesn't give you more capacity, it just reduces time to refill. If you're out for a week and it's very overcast then your lead bank will still die a horrid death, especially given it's less able to make use of the solar that does come in.
