Battery and charger choice for XL-5

[MLJ.pappa]

I am ordering 2 new waterproof XL-5 rustlers for my sons, these new types have metal gears en are brushles ready.
so when they want to upgrade to brushles they have to buy new (lipo) battery's unless these normal motors can handle lipo's i won't buy these normal batt's
that would be great begause i dont have to buy two different chargers, so what do you think?

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And how long do these batt's lasts before the have to charge them again?
And what is the life span of these two?

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Thanks for you help.