Purchase LR44 batteries online from Amazon.com or BatteryMart.com. These batteries are very affordable and are available in bulk for less than $10 as of 2015.
Amazon.com has Duracell LR44 batteries available for about $9 for a 10-pack or $10 for a 20-pack. These batteries have good reviews on the website with 4.1 out of five stars. Though these batteries come from the Duracell brand, they can replace any other LR44 battery.
At BatteryMart.com, the LR44 batteries are not of any brand but cost as little as $0.15 each when buying more than 500 at one time. For smaller quantities, the batteries cost from around $0.75 to $1.