Can I use any USB car charger rated at 10V 2.1A and plug my lightning lead into it?
No, but you can use any quality USB charger rated at FIVE volts. I've never heard of a 10V USB charger; the standard only allows 5 V +- 0.5 V.
That Voltage is too high, 10 Volts will fry your iPhone. But a USB charger with those Amps are fine (those Amps are iPad charger Amp level), it will work perfect at half those Amps too. 10 Watts are iPad charger level which would be fine.
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