Answered by the author of Backtesting.py here

Here's an easy workaround for you: convert the input data to contain prices per one Satoshi (1e-8 BTC) or per one micro bitcoin (μBTC, as below):

df: pd.DataFrame  # Bitcoin OHLC prices
df = (df / 1e6).assign(Volume=df.Volume * 1e6)# μBTC OHLC prices