We know what you're thinking; "What?!". We were thinking the exact same thing. Mugen Power is selling an extended HTC Titan battery that has a whopping capacity of 3600mAh. To put this into perspective (as the above chart does so gracefully), the stock battery which comes with the handset is 1600mAh which has decent performance as is. Should you require that extra juice, or spend extended periods of time finding a charger, this 3600mAh upgrade should interest you.
The only issue is that this will add some considerable weight and a slight increase in width with the included extended battery door/back cover. If you require a battery that lasts up to 2.25 times (according to Mugen) longer than stock, this disadvantage can be overlooked with over 50% increase in performance. Should you not be interested in adding size and weight to your Titan, the 1950mAh battery upgrade (also from Mugen) could be the right choice and will use your Titan's existing battery cover.
Note that this product is currently out of stock and if orders are put through now, delivery will be on February 3rd. The purchase will set you back $98.95.
Source: Mugen Power; thanks, maghedo, for the tip!