Current Handheld Radios (and other devices for that matter) have greatly benefited from today’s Lithium Ion battery technology.
There are definite advantages of this genre of battery chemistries; wether they may be Lithium-iron (LiFePO4), Lithium Polymer (LiPo), Lithium Manganese (LiMn), and finally Lithium Cobalt (LiCo) which is what modern radios use.
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One of the greatest advantages is that Lithium batteries maintain their charge for long. Quality, name-brand, batteries will usually show above 90% capacity, a year after their recharge.
Then there is the advantage of not requiring to be drained down to zero for them to be recharged. In fact you can just recharge them at whim regardless of their remaining capacity.