wouldn't worry about a battery blowing up at 1.8ohms. your kinda miss informing people with this whole blowing up stuff. lots of people use 1.5ohms and up on ego style batts. if you find a battery getting warm then its a warning sign. its not going to spontaneously com-bust lol. no idea why people try and scare others. hes not using sub ohms coils.
This is quite correct.
mAh, a.k.a milli-Ampere*hour, refers to the capacity of a battery to hold power, but it's hardly indicative of what the battery can do. Ex: 1'000 mAh means that the battery can deliver 1'000 milliAmperes for one hour (not that you actually use it that way).
You should keep the same coil, if you want the same experience.
Every battery, regardless of its rated capacity, will have a small voltage drop, as they go from "fully charged" to "time to recharge". This does not change with the capacity; it'll just happen faster with a lower capacity battery.
What's been discussed so far, is that if you use a lower ohm coil, the discharge rate will be faster. Indeed, a lower ohm coil does vape hotter, because it runs hotter. It also draws more amps, which will discharge the battery faster.
Want some math to go with that?
V = R * I
and
P = V * I
Where V= voltage
R=resistance (Ohm)
I=current (Amperes)
P=power (Watts)
With those two equations, you can calculate any electrical circuit, the amps being circulated, and most importantly, how much power you've applying to your e-liquid, as you vape. Given that you have an eGo Twist, you should already know what voltage works for you. An eGo twist maintains the same voltage, regardless of the charge state of the battery. Nice circuit to have, if you have a problem with unsteady power levels as you vape, or if you want more power than what is provided with a standard cell arrangement.
Batteries blow up for several reasons, the main one being damage. The other reason, is by exceeding its rated maximum discharge rate. Max discharge rate is determined by the manufacturer, and is usually expressed as a multiplier of its capacity. i.e. a 10C max discharge rate on a 400 mAh battery, means that it's ok to draw 4 amps from it, until it's discharged.
Exceeding the discharge rate is very rare. Most Lithium-Polimer (LiPo) batteries can handle more than what we put them through. LiFe (Lithium-Iron-nanophosphate) batteries, while a tad heavier, have an even higher discharge rate.
All you need to know otherwise, is that cells should be encased, not out in the open, while using them. A case protects the batteries from damage, and protect you, in an overload situation.
One more thing... batteries are also rated with a lifecycle, i.e. how many times you can recharge them, until they die. Obviously, if you use a lower ohm coil, you'll be recharging that battery more often, and so yes, it will wear out faster.