ratpolish

Grocers do discount short-dated products. Look for the sticker that says "manager's special".

But the batteries don't have a capacity of 0.0385 MW-days. They have a capacity of 0.0035 MW-days when brand new, or 0.0032 MW-days if degraded to 90% capacity. (It looks like they divided kilowatt-hours by 2 instead of 24 to get kilowatt-days.) Not only that, but it looks like off-peak power is about 70% as expensive as peak power, so it'll cost $70 per MW-day to charge the battery.

Year 1 (corrected): 0.0032 MW-days x ($100 - $70) x 365 days = $35.04

Edit: This assumes they're cycling the battery once per day. Presumably there's only one period each day when they can sell at peak and one period each day when they can buy at off-peak.