Update 2015 - Pananic has decided terminate Sanyo brand and now these had become Panasonic Eneloop. Still the best rechargeable batteries in market. These batteries have become cheaper and more powerful. Now you can get 4 Panasonic Eneloop 1900mAh min batteries for around $13 from Amazon. These batteries can be recharged upto 2100 times ! You can see the latest price in ad below.
Both Canon SX10 and Canon SX20 uses 4 AA Rechargeable Batteries unlike models from Canon SX30 which uses ion- Lithium batteries. The most common problem with Rechargeable Batteries is their self dis-charage rate. in simple works if you fully charge set of batteries then after couple of days you find all batteries are dead. Older the batteries get quicker those get dis-charged. Also higher the capacity shorter their holding rate. I have used so many types of AA Rechargeable Batteries for my Canon SX10 and found most of these doesn't hold power long. That's until I tested Sanyo Eneloop AA Rechargeable Batteries. Now I can say without a doubt that Sanyo Eneloop AA Rechargeable Batteries are the best for Canon SX20 and SX10 you can find in market. These batteries stay really really long time and hand hold power for months when you don't use.
I have 4 sets of Sanyo Eneloop 2000 mAH AA Rechargeable Batteries. If newly charged usually need only one set of a one day trip. I would take 200+ photos and I'm you can take at least 300+ photos with one set. I just keep another 2 sets just in case. Also I do have 2 Eneloop battery chargers. One standard battery charger and one 8 hour quick chargers. I haven't had single battery problem ever since I have started using Sanyo Eneloop Rechargeable Batteries. So I can tell you with 100% confidence that Sanyo Eneloop is the best Rechargeable Batteries out there. Whatever you camera models, if it use Rechargeable Battery then use these. You won't regret. My oldest battery set if already 2 years old and still working great. Still these batteries have a really good self dis-charge rato.
One word of advice, always use same brand battery chargers. It helps you to keep battery lift longer. This is just my experience. This is why I bought 2 sets of chargers when I bought first 2 sets of batteries. Also it's cheaper too. You can buy the charger and 2 batteries for less than $20.