Price Check Craftsman 24V 20 inch cordless lawn mower acid battery

[jgy2001]

I purchased the Craftsman 24V 20 inch Cordless Lawn Mower. The model number is Craftsman model 6073290.
In the Sears Parts Direct web site, the battery assembly drawing shows two batteries (I assume in serial connection).
This 20V 20Ah acid battery assembly part number: 31103237-4 Substitution: 31103237-1. Price is $104.19
Can you please tell me what kind of single battery is this? Can I find replacement for each battery itself instead of the entire battery assembly?

 

[jgy2001]

do hope some one out there can tell me what is this battery and where I can buy another replacement battery.

thank you