Rred
Contributor
With SLA batteries, generally speaking the weight of the cases is the same and differences in the gross weight mean one or the other has more lead, more plates, more real capacity. If the plates are thin (as in a car battery) you get a lot of impulse power but more fragile plates that take more damage during deep cycles. If the plates are thick (heavier) they are more robust. They will have proportionately less impulse power, but that's how deep cycle batteries are made.
Even deep cycle batteries are deceptive though. If a battery is rate 40AH, that means typically the battery may deliver 50-100 cycles of that much power. But if you only draw it down to 20AH, you may get 1000 cycles from it. A HUGE difference in the life cycle. And drawing it down to only a 30% discharge state (12Ah consumed) you might get 2500 cycles.
The advantage to lithium-ion is that they normally can provide 2000+ cycles at a discharge of 80%. So a "40AH" lithium battery could be draw down 80%, 2000 times. A comparable lead battery of the best make might provide 200 cycles at the same depth. Lithium becomes much cheaper when you run the numbers for the life cycles and discharge depth. Assuming it is properly charged and maintained, because that's also different from lead.
Even deep cycle batteries are deceptive though. If a battery is rate 40AH, that means typically the battery may deliver 50-100 cycles of that much power. But if you only draw it down to 20AH, you may get 1000 cycles from it. A HUGE difference in the life cycle. And drawing it down to only a 30% discharge state (12Ah consumed) you might get 2500 cycles.
The advantage to lithium-ion is that they normally can provide 2000+ cycles at a discharge of 80%. So a "40AH" lithium battery could be draw down 80%, 2000 times. A comparable lead battery of the best make might provide 200 cycles at the same depth. Lithium becomes much cheaper when you run the numbers for the life cycles and discharge depth. Assuming it is properly charged and maintained, because that's also different from lead.
