Toph said..
I'm about to replace my boats house batteries and I'm considering lithium.
I wasn't necessarily going to go this route except that I've stumbled across a reasonable deal and my current battery charger is compatible to charge lithium. My concern is, do I need to also replace the alternator to a specific type, or will an 80 amp/h alt be sufficient to avoid over heating?

I looked into this but decided not to go lithium as I had one battery that I brought for testing fail. I purchased a victron 12 v to 12 volt charger so the lead acid start battery that takes the alternator charge can then charge the lithium house battery's at the required settings. I would recommend not purchasing cheap lithium battery's.

Toph said..
I'm about to replace my boats house batteries and I'm considering lithium.
I wasn't necessarily going to go this route except that I've stumbled across a reasonable deal and my current battery charger is compatible to charge lithium. My concern is, do I need to also replace the alternator to a specific type, or will an 80 amp/h alt be sufficient to avoid over heating?

Hiya Toph,
If you buy the car replacement style batteries it'll be fine as they have an integral BMS or controller. Your voltage reg will think its a normal lead acid in that instance.
But otherwise yes, you should have a controller. The alternator isn't the issue per se, it's more the voltage regulator. Lead acid has a much higher internal resistance than lithium so it can put up with a 'dumber' charging system. Lithium is easy to screw up if you don't control the charge rate.

The problem with the Lithium drop in replacement batteries is you are relying on the bms to protect the battery, if it fails your battery is toast. Setting them up without relying on the bms for protection but as a secondary back up is a better way to go.
The bms in the cheaper lithium batteries are not very good and can fail easily when overcharged.
Lithium does not handle being overcharged well.
I have 4 x 200amp lithium batteries in my motorhome, 24v bank, set up to charge on solar, bulk charge only at 28v , no absorption or float and they are happy at that, anything over 28v they don't like.
You need to look at it from a cell level not whole battery level, cells 3.2v, max charge voltage 3.65v so set it back a little to account for system tolerances and charge at 3.5 or 3.4v and your batteries will last a long time and still be charged to 95-99%.

Ok, thanks all for the replies. I wasn't even thinking about overheating the batteries (even though I new they could), but was more thinking about the alternator.

I was watching a clip where lithium batteries where being charged by a normal alternator and the alternator temp was being measured. I don't know what size alternator was being used in the test, but it burnt out when at idle speeds. It was significantly warm at higher RPMs, but didn't burn out as the cooling fins where doing their job. While the purpose of the clip was to sell a specific brand alternator replacement, it did leave me wondering if a larger alternator would handle the temperatures better, or would that create a higher charge rate and therefore overcharge/heat the batteries.

Southace, with your set up, have you mixed lithium and lead acid?? I didn't think that would be possible.