I suggest that you use your own judgement on this. You can assign a reasonable percentage since it is impossible to monitor the hours using those assets. Example: 40 personal and 60 for business. It's really your call.
I also suggest that you should be conservative on valuing the assets. Record the assets at it's lowest value. This is one of the most difficult scenarios in making your own financial statements.
You can also use this approach, i will record the assets at its original cost then use a higher depreciation rate or double declining method of depreciation. If the assets have a depreciation rate of 20% per year (useful life of 5 years), i will make it 30%. the other 10% will add more expense and helps you not to overstate your Financial Statement.
You can also use the residual value of the asset, but if you do this, you should figure out the reliable amount.
I understand that this is not for tax reporting purposes. Therefore, there's no harm if you overstate your Financial statement. And even if you overstate, you can still adjust the cost of the asset. Along the way (in the middle of the year or year end), you will figure out the cost of the asset if it's over valued once the financial statement is done.