Or you could buy a 40D or 5D and get another charger for "free"
Maybe thats not funny but one came with my wifes 40D and I was happy they took the same batteries
I have one f the sterlingtek chargers and it has a little led flashlight and a cig adapter (the reason we got it)
There is a third party dual charger for BP-511's sold under the Impact brand name by B&H. The model number is DP-BCB and it is around $70. It comes with the ability to work off of either 120 V AC or 12 V DC.
Getting another single charger, either a Canon brand one or third party, is likely your best bet, and still allows both batteries to be charged at the same time.
Did you know the OEM dual charger only charges ONE battery at a time? You can obviously insert two batteries, but it charges one and then the other sequentially, not simultaneously.
dcains was right, even though you can put 2 batteries at the same time, it still charge it one by one.
Maybe the best advantage is that you dont have to keep checking at it and put the other battery when the first one done.
I'd suggest to get batteries/charger from sterlingtek.com, they are cheap and good.
I have 10 BP-511 and about 4 or 5 charger, so I can charge them 4 or 5 at the same time, so it safe more time compares to only charge them 1 or 2 at the time if I only have 1 or 2 charger.
stefthetoolman, in your case, just get 1 more charger from sterlingtek for around $15 and thats it, youre done, you can charge your 2 batteries at the same time, and at the same time save around $150 compares if you buy those Canon dual batteries charger for $179.
The best move would be to buy 4 sterlingtek batteries and then keep them all charged but use the single charger. Doubtful you would ever run out or even get close to it.