I was put off by this at first with my RX100, but now I love it. I just plug in the camera, and I travel much lighter. BUT I haven't hit a point yet where I shot so much I ran out of battery.
I regularly run down at least one battery when shooting such that I always carry at least a second charged pack (and another SDHC) card with me even when travelling light one camera one lens. With any luck that won't be necessary too often but I'll keep the habit going.
Additionally, I did purchase a 2nd battery, but I've not even recharged it one yet, because of this "keep in camera" approach. I'll need to start using it, just to keep it alive, so I can have 2 batteries when I really need them.
Guess what... you don't need to keep a lithium ion pack fully charged to "keep it alive".
Quite the opposite in fact -- keeping cells at or close to fully charged all the time is the surest way possible to shorten their life span. Cell / pack makers ship cells / packs partially charged for good reason - they don't want them to age prematurely while sitting on shelves and warehouses.
Another fact worth knowing - don't buy too many packs, more than you can reasonably use. I find I need to cycle three packs with my GXR - I number them 1, 2, 3 and use them in order and when I'm not travelling usually always have one charged in camera and in my bag. The other might remain partially charged for "storage" at home.
Li-ion cells have a finite lifespan whether they are used or not. Age is measured in how many years and/or cycles a cell/pack can hold a charge of at least 80% of original. As the cell technology has improved we've seen good quality packs easily last three or more years if they are treated well; five years is not out of the question. How long a pack lasts before it is time to dispose of them depends also on how heavily they are used, which really means how many charge-discharge cycles a pack goes through.
A pack that gets depleted and then fully charged again, used, fully charged again and so on might for arguments sake have a cycle life of 250 to 350 cycles. That's a lot of photos for many photographers.
However a pack that isn't stored at full charge all the time in between shooting sessions may well last 300 - 500 cycles or more.
For maximum pack life it is better to avoid the temptation to plug in the camera for a charge session every time you finish using it. Allow the pack to deplete not so much as to "exercise" the pack but to give the pack more time at voltages below full charge.
In short, if you have room to carry a spare pack safely[1], don't recharge the pack in-camera unless it really needs it. Swap packs and run down the other one. Charge as you need to in order to feel confident you aren't going to be left high and dry when you want to shoot.
[1]I keep my spare packs in small plastic cases about the same size as the pack itself, such that they can't short out against keys, coins and other items that might be in my pockets, camera bags, day packs and other places I carry cameras and packs.
Avoiding a short is very important. A lithium ion battery pack carries a huge amount of energy which is of course dangerous in the case of a short, and while all consumer oriented battery packs (like camera packs) should / must have thermal and electrical safeguards against a dead short, you don't want to take the chance.
Ooops... part of my other life snuck in there. Lecture off.