Hi, and welcome to RCU. This topic gets debated over and over. Yours is unique because of the significant difference in capacity. One thing that it has going for it is that is not being operated at or near the max current capability. All things aside, I think it'll work just fine.

I can leave it to the others to list the reasons it may not be good. One thing is for sure the voltages will always be equal. Here's one question that may help to proccess this.

Is the larger of the two batteries sufficient to do the job?