There's no mains power on the mountain, unless you count a few huts on the Marangu route where charging is sometimes sold. Plan as though there's none.
Power banks, and more of them than you think
Two decent power banks for a seven-day climb is a sensible starting point, more if you're shooting a lot of video. Check your airline's rules before you fly: lithium batteries go in hand luggage, never in a checked bag, and there are limits on capacity. A small solar panel strapped to a daypack sounds clever and is mostly disappointing, because you're often in cloud and the panel spends the afternoon in shade.
Cold eats batteries
This is the part that surprises people. A battery at minus fifteen reads as flat and then recovers once it warms up. So keep spares in an inside pocket against your body, not in the pack, and take them into your sleeping bag at night along with your phone and your camera. On summit night, carry the camera inside your jacket and bring it out to shoot.
Is there phone signal?
Patchily, yes, and more than you'd expect. There's coverage on parts of most routes and often something at the summit, which makes for an expensive photograph if you're roaming. A local SIM bought in Moshi or Arusha is cheap. Don't rely on signal for anything that matters, and do tell people at home you'll be out of contact, so nobody panics on the day you're in a valley.
What camera to take
The honest answer is the one you'll still be willing to carry on day six. A phone takes excellent photographs and weighs nothing. If you bring a proper camera, bring one body, one lens and a cleaning cloth, keep it somewhere you can reach without stopping, and accept you'll shoot less than you planned. Above 5,000 metres, getting a camera out of a bag feels like a lot of effort.
Condensation
Bringing a freezing camera into a warm mess tent fogs it inside and out. Put it in a plastic bag before you go in and let it warm up slowly.
A head torch is the real electronic
You'll use it every night and for the whole of summit night, in the cold, for hours. Bring a good one, bring spare batteries, and put fresh ones in before summit night rather than finding out at one in the morning.
Drones
Don't assume. Drone use in Tanzanian national parks needs permission arranged well in advance, and turning up with one unannounced is a good way to have it taken off you at the airport.
Watches, trackers and the summit photograph
GPS watches work fine and the altimeter reading will wander, because they're pressure-based and the weather moves. Battery life drops in the cold, so turn off what you don't need and charge from a power bank at camp. And decide before summit night who's taking the photograph at the sign: it's freezing, hands don't work, there may be a queue, and the light at sunrise lasts minutes.