Switching from SLA 48V 100AH to Lithium - do I need to stay at 100ah or can I go 50ah?

[jdy2kgt]

I'm getting ready to switch my electric boat from SLA to Lithium. The system is 48V and the SLA had 100AH. But as we all know with SLA you only use 50% capacity. This got me thinking since Lithium can go to 80% do I still need 100AH or can I save a lot by going with 50AH? I also have 440W of solar that is feeding/charging these batteries when the sun is up.

Here's my math - does it look right:
SLA - 4800 watts - usable 2400W, motor normally draws 10.5Amps = 4.76 hrs of run time
Lithium 100ah - 4800 watts but at 80% = 3840W usable, drawing 10.5amps = 7.62 hrs of run time
Lithium 50ah - 2400 watts = 1920W = 3.81 hrs of run time

Obviously, if my math is right I can see the 50ah I would be about an hour less than I was on perfect SLA's, but with the solar doing its job does it matter?

Thank you for your thoughts.

 

[Rednecktek]

100ah batteries will take up about the same footprint but be less than half the weight.

50ah is a step down in capacity.
"I have too much battery capacity" said Nobody Ever. Having the extra capacity gives you some energy to play with if you want to add in something electric later.

 

[Pi Curio]

I'm getting ready to switch my electric boat from SLA to Lithium. The system is 48V and the SLA had 100AH. But as we all know with SLA you only use 50% capacity. This got me thinking since Lithium can go to 80% do I still need 100AH or can I save a lot by going with 50AH? I also have 440W of solar that is feeding/charging these batteries when the sun is up.

Here's my math - does it look right:
SLA - 4800 watts - usable 2400W, motor normally draws 10.5Amps = 4.76 hrs of run time
Lithium 100ah - 4800 watts but at 80% = 3840W usable, drawing 10.5amps = 7.62 hrs of run time
Lithium 50ah - 2400 watts = 1920W = 3.81 hrs of run time

Obviously, if my math is right I can see the 50ah I would be about an hour less than I was on perfect SLA's, but with the solar doing its job does it matter?

Thank you for your thoughts.

Food for thought.
'A' grade 105Ah cell is about 45% more expensive than 50Ah, but the gain is double the capacity.

 

[yabert]

....or can I save a lot by going with 50AH?

Save a lot? Well, with a lot of cells/battery sell around 100$ / kWh, we only speak about saving few hundreds $
Maybe start to look at high quality used EV battery module and you could be surprise how affordable they are.

Your main gain will be weight. By example, some 48V 100Ah lithium module can weight as low than 50 lbs ?

 

[jdy2kgt]

Thank you everyone. You've convinced me to stay at 100AH.