can you charge it without having to use the cup?

The included travel case can also charge. Also only the silver base of the cup does the charging. So you can remove the glass cup from the base to just store the toothbrush.

I currently have a perfectly good e-series essence, is it worth the $ to replace it with a diamond clean?

I could not answer that honestly, i have never used a e-series essence. The diamond clean is my first non manual tooth brush. I did do research of the sonicare line of brushes, and what i found was the diamond clean had solid results. The different modes of cleaning (5 settings Clean- For exceptional everyday clean, White - Removes surface stains, Sensitive- Gentle teeth and gum cleaning, Gum Care- Gently massages gumsDeep Clean ) , battery life ( roughly 3 weeks a charge ) , power the brush has to clean (62,000 strokes per min) and the charging case you can plug into a USB and charge from a lap top (great for when i travel). The brush is very easy to use after the 24 hour recommend first charge time. The brush will pulse letting you know its time to switch from top to bottom row ( each setting has a timer, clean about 2 mins broken down into 30sec outside/inside of teeth top/bottom row . Only after a few weeks of using the Diamond clean i already feel a difference in my teeth, they feel cleaner, stronger and healthier. Whiteness? I can see a small difference but no one ever really notices a change in themselves. I did try to find the best deal, the web site has i believe at the time 20-50% deal. AMAZON for me was the best deal at the time ( $187.99), that sounds high but in terms for dental bills/pain later on i felt it was worth the money (especially with a warranty that the company provides ) Any more questions feel free to ask.

How about the voltage? Is it 110V-240V?

Philips website for all (I checked 4 of them) Sonicare brushes says 110-220V. Most AC>DC transformers (think cell phone chargers, laptop chargers) automatically handle 110-220, and that's probably what's in the base of the chargers here. The things that take AC power directly (i.e. hair dryers) and don't have a DC transformer are the things that aren't automatic... (sometimes the hair dryer will have a switch on it so you could plug it in to a different voltage outlet, but still requires you to do something--not automatic)

What speeds does it have?

5 SPEED AWESOME BRUSH! Also travels very well, we were out for 11 days w/o requiring any charge. (All travel supplies are included case and charging cord) I highly recommend this product A#

Item model number	HX9372/04
Product Dimensions	11.1 x 17.4 x 25.2 cm; 1.04 kg
ASIN	B00YAR7Z70

Philips Sonicare DiamondClean Sonic Electric Rechargeable Toothbrush, Amethyst, HX9372/04

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