3v 225 mAh is not what it pulls. That's the battery rating. "Pulls" refers to the current at a voltage. For example, you may say that it pulls 100 uA at 3v. So, first step is to measure what it actually pulls. Ideally profile it over time and in different scenarios. Or record how long it takes to drain the battery, measure the battery voltage under a small but nonzero load, and approximate how much energy was drained vs time to get watts consumed. Then you can work out what kind of solar cell and charge controller you can pair it with. Unsure if MPPT would be needed here, you likely aren't going for the absolute max power efficiency.