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@freemo liion for standardized size and longlasting
@wilmhit by long lasting if you mean the number of times you can recharge it then its about the same as NiCd and NiMH in that respect. Lithium metal has, however, about 2.5x or more recharge cycles.
This all assumes you only let your battery discharge to 50% at most. If you discharge to 100% Nickel Cadmium actually has the longest life span.
@freemo I always had opposite experience. I'm not a professional. I only repair my home appliances as a hobby. From my experience liion lasts the longest but this may be due to greater capacity/shallower cycle. I don't do li metal cuz I like 18650.
@wilmhit Its a bit more complicated than that. NiCd has memory the others dont (well NiMH has memory too but its much less noticeable). That means that when it doesnt fully discharge over time it appears as though it is end of life by having a much reduced capacity. In fact this is not a permanent position. The memory of a NiCd is caused by crystallization that is reversible by deep cycling it a few times.
In all liklihood you are seeing the memory effect rather than an end of life scenario.
Li-ion of course has the highest energy density, so that can sometimes make up for the fact that it has fewer cycles since you get more power per cycle.
Lithium metal comes in 18650 just like lithium ion batteries. In fact I'm charging a pack of 18650 lithium metal batteries as we speak
@freemo ty sir very informative. I'll look into modding my roomba from 18650 liion to limetal
@wilmhit the big difference is the charging circuitry. Liion and liFePO4 have similar charging curves but different nominal voltages (3.7 vs 3.2). So they arent always drop in replacable. With that said most smart charging circuitry can detect the two and charge both, even some of the cheap stuff you wouldnt expect to be "smart" seems capable
Just make sure the voltages are ok and you have the right charging circuitry and you should be good.
That said lithium ion and lithium metal are similar enough it might not be worth the hassle to mod it. But if you are building something new I'd personally always lean towards lithium metal out fo the two.
