With lithium do we actually need a dedicated starter battery?

[CaptainRivet]

With LFP and the tight monitoring and massive current capabilities do we really need a dedicated starter…a LFP house at 2.8V can easily start the engine several times…a depleted AGM can‘t.

Where did a seperate starter actually come from:
Simple answer a lead battery is either
1) a deep cycle for storage, that cannot deliver high current otherwise you destroy it or
2) a starter that can deliver short terms high current but you destroy it if you take constantly current off.
Additional the leads needed to be always full to have full CCA or current capabilities, at a lower SOC they are much worse and if not charged full die very quick. Add to that Peukert effect means the more current you pull the more weak the lead gets and voltage sags deep cause devil cycle more current….
Additional monitoring a lead is still not a secure method to know it’s ok as eg a dry lead still shows the full voltage but as soon as you put a load it collapses.

With lithium this is all completely different.
Already most 100AH LFP can start an engine, 200AH LFP house can easily start your engines, if then BMS is the limiting factor.
A LFP is very tightly monitored and every second you know exactly the real!!! state of your battery.
Conclusion:
There is absolutely no reason not to start from your lithium house bank your engine…it’s actually beneficial as the house is normally that big in AH that it’s kindergarten for the cells to do, means you are at 0.1 till 0.3C and wear on the starter is much less as enough current capabilities and no significant sag in voltage. House is always in use so you know it will 1000% start your engine and you have no surprise of a dry dead starter that collapses when you put a load on

Redundancy:
A lead lives a short live (300cycles max) and is unreliable in monitoring, sure you need redundancy in having a starter that just does this job.

A lithium lives much longer 2000-8000cycles and has a reliable monitoring.
A lithium bank consist of several single batteries in parallel so you already have redundancy.
For a costal sailor which are mostly the small boats too and space is a premium that hybrid LFP house has enough redundancy and reliability compared to a lead setup and as you are close to shore and in the really unlikely event you get fast help if needed

For bluewater cruiser or boats often far way from coast still redundancy is good and senseful requirement but having sitting around a starter that 98% of time does nothing, you don’t know if it really works if you need it and is of no added value then just sitting around waiting to be ever used.

is it not time to modernize and change these concepts as the reason there was seperate starter and house bats is completely gone with lithium.
My clear answer is yes it makes sense and is long overdue.

A much better approach is a buffer battery as redundancy:
It’s much better to have a hybrid starter house bank and a buffer battery (LTO or LFP or AGM) which by default is always full (or near full depending on how you set BMS if LFP) and that isolates and serves as independent power source for our nav equipment at navstation and helm.
that buffer battery is always in use, so you know it’s working and always full or the SOC you target. besides being small AH if LTO or eg Winston cells or an LFP starter bat it is still able to start engine in emergency case, so you have your redundancy and know your redundancy works if needed.

To me much better setup, cheaper, simpler and solves a lot of issues you have with a dedicated starter.
No need for a lead starter ever again.